Solo air is a single valved chamber which internally divides into negative and positive but remains balanced at a sensible level. Dual air has separate chambers and increases the amount you can tune your fork. Many people end up with a similar setting to the solo default but you can bias the fork behaviour to either small bump compliance or more pert but able to deal with wallops without diving as much.
Then you have dual position, which as it sounds lets you drop the front end by flicking a switch on the crown and bouncing, to reduce the front by 30mm. This is great for climbing/milder terrain.
One argument is that more adjustment is more to go wrong, another is fettle, fettle and fettle some more!
I’ve had positive experiences of dual air Revs and Pikes but settled on about 10psi more in the negative spring after much trial and error, which is fairly common. I now use a solo air, dual position Rev and it’s great.
So, it depends on how much you fiddle with your front end or how diverse your riding is. Dual gives you more options, but it’s much of a muchness if you’re unlikely to take the time/effort to explore these.