I don't usually review items the day after I receive them, but with tubeless tires ease of set-up and air retention is a huge aspect of the tires overall usefulness.
Vittoria really did it right with the Terreno line. The bead on these is tight, but not unreasonably so, and seems to stretch ever so slightly to allow installation without breaking a knuckle. The tires snapped into place on the first try with a compressor with a loud and confidence inspiring pop. My favorite part as a bigger guy is that they immediately held air without multiple times pumping them up, adding more Stans, shaking and spinning them around, etc. After the very first time they were pumped up the tires each held 85 psi for 12 hours without losing hardly any pressure. This is a big deal to me after dealing with other brands.
Relative to others, I've had very good luck with Schwalbe but they are a b&tch to get on, and also positive results from Hutchinson, Donnelly and Panaracers. On the other end, the new Challenge Gravel Grinder tubeless were a little disappointing and do not hold air well. Great riding tire, but tubeless performance did not stack up.
I'll post a full review soon, but my initial impression was positive enough to merit posting already.
These are the real deal. Fast on pavement and flat roads, grippy enough on punchy gravel climbs, confident on descents. I really am psyched about these. I had resigned myself to running slicks on gravel in the summer to keep up on fast mixed surface rides with friends but these are much better. I still like my Sector 32s but the Vittorias are just as fast on flats, and miles better climbing and on gravel descents. I've also tried the G Ones which I have nothing bad to say about, but the extra grip seemed nominal to me over slicks and the G One has a little bit of a weight penalty (obviously if its wet and muddy anything is better than slicks, including the G One). The Vittorias, though, provide everything I am looking for with limited compromise. I even set a PR on a tough rolling sprint climb chasing down the local club group ride on my cross bike just to see if I could. These tires really roll exceptionally well on pavement for the grip you get on more variable surfaces.
Oh, and they still hold a TON of PSI without leaking. Easily the best tubeless performance I've experienced.