I have used the spray stuff. Works well in my experience, as long as you follow the directions i.e. don't overspray the fly and let it dry before fishing it. The first floatant I used was Gink, and I ended up switching to the spray stuff sold at Walmart because it was cheaper. Seemed to work, maybe not as well as Gink, but it did work well.
A bad day hunting rabbits beats a good day of anything else!