I'll answer this as carefully as I can.
I've tried the three popular systems, Radian, Skyline, and Hoverfly Gimbal. All three of these controllers are built by people that are passionate about the products they're building and have put tons of hours into them. In my experience, each is backed by good people that have been very helpful.
The Radian is the most expensive, but it is worth the money. Setup is soooo easy. Software is easy to use. It always works - very reliable. I was a beta tester for the Radian, and it worked well from the very beginning. It's also got a lot of features, and those features don't get in the way of the functionality - they don't complicate things. At first glance it's simple, but then you realize that it is very customizable if you want it to be. I like that.
I'm about to test the recent firmware of the Hoverfly Gimbal, so I'll hold off on my comments on that one. I've used it with success in the past. I'll report back with current results soon.
Some people have had great success with the Skyline - I'm not one of them. Not sure why I couldn't get it working, but I couldn't. I'm not bashing it here. I just gave up after about 12 hours of fooling with it. Could've been user error.
I prefer the Radian system.
Please note that I've received each of these for free from all three companies, so that kind of eliminates any bias based off price.