Are you using a hardware based raid controller with them?
Yes, of course. Hardware raid with cache and bbu is a must. You can't get fast fsync without it.
Most SSDs should offer fairly fast fsync without a hardware RAID controller, as they do write-back caching. The trick is to find ones that do write-back caching safely, so you don't get severe data corruption on power-loss.
Actually most of low-end SSDs don't do write caching, they do not have enough ram for that. Sandforce for example.
A HW RAID controller is an absolute must for rotating magnetic media, though.
Also mdadm is a pain in the ass and is suitable only on amazon and other cloud shit.
I've personally been pretty happy with mdadm. I find the array portability it offers very useful, so I don't need to buy a second RAID controller just in case my main controller dies and I need a compatible one to get the array running again. If you don't need a BBU for safe write-back caching then mdadm has advantages over hardware RAID.
If we are talking about dedicated machine for database with ssd drives, why would anybody don't by hardware raid for about 500-700$?
I'll certainly use mdadm over onboard fakeraid solutions or low-end hardware RAID controllers. I suspect a mid- to high end HW RAID unit will generally win.