The convex buttons are almost certainly Competition buttons.
The concave ones are more than likely ‘Pushbutton with Horizontal Microswitch’, as they’d need much less maintenance.
See, over time, the Ultimate buttons will weaken and can actually break, needing to be replaced completely. I was witness to this occurring at precisely the wrong time for the stick owner, as he was preparing to play in a local tournament I was at. It was a MAS model, and they use Ultimates for their concave buttons (ProTip: if you’re going to order from them, get Competitions and swap 'em out for the horizontal concaves if that’s what you prefer).
Competition buttons and the concave with horizontal both have the same pressure requirements to activate. The only difference in feel is the button shape, and that’s more of a personal preference.
Anecdotally, though, I seem to have more trouble pressing the two Competitions in my modded SFAC at the same time as compared to any two of the concaves I have in.
That brings me to another point. If you don’t mind getting a converter for PS3, getting a Street Fighter Anniversary Collection stick that’s been modded with Happ parts is great for a starter stick. Unfortunately, its stock parts, with the minor exception of the stick itself, are inferior chinese knockoffs (the stick is a pretty decent Super clone, but it pales to a real Competition).
Going custom is the other option, but be prepared to possibly wait for a slot to open up. Good builders get swamped with requests, and some get backlogged for several months at a time.
Hope this info helps ya, man. Peace.