I've got about a year on the Onyx SC in 27.5 flavor. Came from a 2017 Fox 36 RC2, with some time on a Lyrik from a few years ago. I'd say the DVO is a little less refined with occasional noise from the OTT negative coil spring near top-out (don't notice it riding), but plusher, stiffer, supportive, more durable, and easier to work on. Biggest current DVO downside is lack of offset options and the odd almost-at-top-out noise/clunking in the parking lot. Biggest positives are reliability, and combination of plush and supportive.
Durability: The DVO is a lot more durable than the 36, which is why I made the switch. I was one of the people that would kill CSUs every few months. DVO is a little heavier (200-ish grams), which is what I wanted for my trail/everything bike. The DVO also runs 40cc of bath oil in both legs, which is freaking awesome for keeping it feeling good when it's not fresh.
Damping: I was super happy with the Fox 36 RC2, but the DVO feels great. DVO stuff is generally lightly damped, so I run the LSC at 3 of 6 all the time, where the Fox was close to open. The Onyx LSC adjustments could be finer, I really only use the #3 setting. I run HSC fairly close to closed (1/3 to 1/4 out), where the 36 was set fairly open, plus a bottom-out token. The Onyx is really well controlled, I quite like it, but the Fox has more usable adjustments and LSR + HSR, while the DVO is LSR only. No complaints with the Onyx default HSR shim, it's where I want it as an aggressive 190lb non-racer, handles bomb-holes and flat landings nicely.
Air spring: I quite like the DVO, but also liked the Fox. Wasn't a fan of older RS air springs, they felt wallowy. I've got the Onyx set a few psi more than they recommend, and the OTT 9 turns in to add plushness at the beginning stroke. I ran 6cc extra oil in the air chamber at 160mm, now at 170mm I'm running it stock. Lots of mid-stroke support, which is sweet. DVO wins on this one.
Service: DVO crushes the Fox here. Lower leg service is easy with no special tools. Fox is easy, too, but you need to be morecareful knocking out the threaded pieces when pulling the lowers (get the expensive lower removal tool for the damper-side). Rebuilding and bleeding the damper is super easy on the DVO, which saves $170/year. I just had to make a damper cup thingy from a Nuun tablet package (or buy the bleed cup from DVO). I always found the FOX RC2 rubber bladder was totally bungled after a year, Grip2 probably fixed that. I eventually stopped doing my own damper service on Fox so that I could get new CSU every time I sent it in to Fox.
The only thing that is fiddly on the Onyx is changing travel, but at least the travel spacers are cheap. DEFINITELY buy a burly automotive-style pin spanner like this one or you'll wreck shit. It's easy once you have this tool and some Loctite. The DVO spring-side lower oil does look uglier than the Fox ever did when I service them about 3x/year, but that's because it's mixing with grease from the OTT spring. I'm fine with that.
Support: DVO (in the States, at least) is second to none. A tech guru (Ronny, from back in the Marzocchi days) actually takes your phone calls, doesn't bullshit questions when asked, and will even give you advice on re-shimming (needed on the original Jade shock, which I didn't like and sold). Most parts available on their website and not a ripoff.