Controllers are necessary to do roaming well. Wifi clients get to decide which AP they want to talk to, and if they're connected to one they don't usually go looking to connect to another until they lose the signal entirely. So if you're on your phone and walk across the building, you'll still be attached to the original AP even though you may be standing next to a much stronger signal. A controller can notice this and bump you off the original AP so your phone connects to the strongest AP around.

Controllers are also just convenient so you don't have to do the same setup N times.

I've used both Cisco and Ruckus, and I'd probably go with Cisco at this point. I would have tried Meraki before they got acquired by Cisco, but would be a little hesitant now. (the Ruckus controller didn't do roaming two years ago - it's possible it does now. Ruckus is really aimed at large outdoor coverage areas - cisco is aimed more at dense office buildings)