I'll add some real world experience. My vote is for Ruckus Wireless.
The R600/610 was mind blowing good. The range and speed capabilities at this time were second to none. They could also handle a TON of traffic too. The R650's seem to have less range than the previous models though (that's a discussion for another day/thread).
In theory the wireless clients are supposed to make the choice of which AP they choose based on several factors. But there are lots of wireless clients that once they get a signal they hold on to it for dear life, even if there is a better AP with more signal.
I have a client who did not want to upgrade their wireless cameras, it was supplied by a ISP, they couldn't get out of the contract and just decided it was easier to keep them for the time being. These cameras quickly became the bane of my existence! I installed three access points in a house. staggered across three floors for optimal coverage. I had two of these wireless cameras that despite having an AP installed within 10 ft inside the garage they insisted of connecting to an access 3 stories below them, in the dirt, in the basement level of this house. The physics were just dumb that it could see and connect to the wrong APs. When they would connect to the garage access point they had -65db signal or better, when they connected to the basement AP they had -90db or worse. They'd stop responding to pings, they wouldn't function but they just never switched back to a good AP. For whatever reason these stupid wireless cameras would always hop over to the worst signal for no reason.
Ruckus Wireless has a feature called Smart Roaming (it's available on unleased and ZD). It's designed for sticky clients like the example from above. It's works on a range of 1 - 10. We started with a recommended level of 3 and slowly worked our way up to 5 before the wireless cameras would get kicked off the weak AP's and switch back to the AP's next to them.
In unleashed, you have to use the CLI to find it though, it's buried deep in the controls. it's not available through the web GUI.
There's lots of examples of wireless clients not following standards and being sticky wireless clients. Apple products sometimes aren't the best either. Just because they say the follow the standards doesn't mean it actually happens in real world examples.
Bottom line, when you have sticky wireless clients, The ruckus Unleashed and/or Zone Directors can force the wireless clients off the network and re-authenticate to better APs. The controller can monitor and force wireless clients to roam between access points if/when configured.