Fiano di Avellino and Greco di Tufo are the obvious suggestions, but also less well-known wines; Falanghina from the Benevento area, Falanghina from the Campi Flegrei (a different variety, confusingly), some whites from Ischia, some wines from the Amalfi coast.
Anyone who likes eg Chablis should at least try some of these wines. Fiano di Avellino certainly ages well, too; I’ve had 10 year old examples that were excellent.
Bierzo
FWIW -
My vote: Australia
I know some of the discussion about this choice will start with “Wait, what? Australian wine is well known and highly regarded. There are better-deserving places so WTF?”
Hear me out.
I believe that Australia is under-rated exactly for that reason.
Big, bold, powerful Shiraz - well understood.
Cheap and large-format/box wines - well understood
Exceptional other varietals - barely see the light of day or get the attention they deserve (hence the underrated tag)
During my time in the trade, selling an Australian wine other than to a big Shiraz drinker was an incredibly difficult task. “They’re too bold” or “I only drink Cab” quickly relegated Australia’s other choices to also ran’s - even during an assisted sale to a knowledgeable drinker. To the casual wine buyer, the “yellow tail” effect set an equally immutable though opposite perception of the region.
I believe the non-Shiraz and mid-tier wines from Australia are the most underrated region today. Cabs, some pinots and a variety of white and white blends are phenomenal. The private brand available in Australia is also a source of innovation that rarely extends outside the region.
If you haven’t had some of these underrated Australian offerings, I’m not surprised. My other argument for Australia’s under-rated status is that the wide variety of offerings available in Australia does not get distribution in the US. As a consequence, these wines are in a vicious cycle - they don’t get distribution because of their perception and their perception can’t change without better distribution (and marketing).
Just my 2cents
BTW - 3 of my top 10 wines ever consumed are Australian so I’m probably a bit biased here… but I believe my logic holds (and no, my fondness for Crocodile Dundee has not influenced my viewpoint)
This basically mirrors what I’ve been saying about Argentina. Not that I am saying either of these are the most underrated, but they do fall into what may be called widely misunderstood. I think both of these, and to some extent places like California and maybe even Spain, suffered from what may be called the Parker effect. I don’t blame Bob, I put it on those who fashioned a style that appealed to him and ran as hard and fast as they could with every pointy review. It warped and damaged their reputations.
While our West Coast is considered upper echelon Wine producing regions, let’s not forget the rest of the country -
MICHIGAN: Already producing terrific white wines, especially Rieslings. The reds are coming along.
NEW YORK: Also producing exquisite Rieslings. The reds have also come a long way. And the Finger Lakes is a super fun visit. Don’t expect a foodie paradise, but these little towns surrounding the lakes are beautiful, and it seems like everyone has a waterfall.
NORTH CAROLINA: The Yadkin Valley has really come a long way. Petit Manseng for one is a highlight. The best vineyards are quite spread out, so it’s not an easy visit, but impressive wines.
COLORADO: The Grand Valley is just beautiful, with rocky hillsides framing the vineyards at every point. The wines remind me of the wines coming out of the warmer areas of California (Lodi), but the top end is producing some pretty good wines.
Yup, 100% agree. Selling Australian wine is incredibly tough since everyone thinks they know Australian wine, yet do they?
Apologies for not being more clear. I as well enjoy Fiano di Avellino, Greco di Tufo and Falanghina. I was not aware that Falanghina from the Campi Flegrei was different!
What I meant was, can you name some producers you like? So far I’ve just bought the 2nd cheapest Falanghina or Greco di Tufo at the local shop and have always been pleased.
Yeah I know being honest with myself that I have a very specific, and not all too favourable impression of oz wines, which intellectually I know can’t be right.
The majority of Australian wines readily available here in the U.K. are however not super inspiring. Strongly suspect the good stuff never leaves Australia.
Now this is a region - unlike Corullon.
I think it’s a bit ridiculous to say a village within one region is underrated or overrated, if there is just one single producer (at least I don’t know any other producer than Palacios) that bottles wines made with fruit sourced exclusively from this particular village.
Not sure Oilver is comfortable touting his own producers, which you can see on his site, but I offer one of his that I used to import a long time ago: Ciro Picariello makes great Fiano. Real terroir in those.
Guido Marsalla makes really nice Fiano too. Both can age well. But there’s a bunch of really nice wines in both colors and at prices that are relatively modest in the region. It’s up there in my picks for most underrated.
Colli di Lapio
It would get a vote from me, too.
I would add Piglio in Lazio. The best Cesanese del Piglio are earthy, complex and can age well.
I think Montepulciano d’Abruzzo is mostly underrated because there’s such a chasm between the really great producers like Valentini and Pepe and the ocean of plonk for which the region is best known. But there seem to be some up-and-coming producers like Ausonio that don’t charge an arm and a leg for high quality wine.
Anderson Valley and Mendocino Ridge are severely underrated. Excellent pinot and sparkling from those regions are flying under the radar.
Mount Eden is by appointment only. Rhys is extraordinary, they now also have tastings by appointment, not inexpensive at $95.
The city of Santa Cruz hosts many tasting rooms. Birichino and Storrs have tasting room away from the main cluster. Birichino has some Santa Cruz Mountain wines but lots from elsewhere. I believe Storrs is mostly or entirely Santa Cruz Mountain wines. In the cluster, both Santa Cruz Mountain Vineyards and Silver Mountain can offer some excellent wines.
I used to think I knew it quite well, but we’ve not visited for over a decade, and purchases have mostly dried up as well. Even when you know what you like, it can be hard to find the likes of Craiglee, Delatite, Juniper, Taltarni etc. over here, and even a big name like Seppelt has been near impossible to find in the UK.
The other aspect of Aussie wine is the amount of change remains high. Unconstrained by tradition and any local appellation / consorzio rules, there are always new ideas being tried out in Australia: new grapes, new regions, new techniques in vineyard and winery. Even the (too often to my tastes, but beloved by critics) ponderous red wines of Barossa Valley and McLaren vale have people changing expectations, of the lightness and vibrancy that is possible. Stand still and you miss such innovation, and I’d include myself in that situation now.
Absolutely … Abruzzo
Right, I import some of my favorites, but there are certainly others; Guido Marsella is great, as you suggest.
Terroir is right, we now have two Fiano di Avellino producers from different areas, and they are obviously fundamentally different, even though both are made entirely of the same variety. Some of the vineyards are limestone-based, some have volcanic layers.
Some of Italy’s best white wines come from the south, which was not at all what I expected when I started doing this, given the French example.
Bündner Herrschaft in Switzerland
Somehow stumbled upon this thread today! And, reading through, I don’t see a single mention of Chile on here, which I’ll take as added evidence that it’s the most underrated 
But given that Chile is a whole country, not a region, I’ll narrow it down to Itata. One hundred year old (and older) dry-farmed vines on steep hillsides, crumbly granitic soils, remarkably expressive, age-worthy wines, both white and red (and orange/amber as well) - and they typically sell for $20-30 a bottle. I have tried some País bottlings from Itata that could easily pass as Alto Peimonte Nebbiolo, but at half the price.
Itata is certainly not the only region in Chile that suffers from the country’s overall reputation (Bío Bío and Maule are also often exceptional and well-priced), but for overall quality, they strongly deserve to be in this discussion…even belatedly.