i usually float, but thats just cause im lazy. I drip occasionally but its kind of a pain.
What i typically do is float things purchased from a LFS and drip mail order live stock (the mail order livestock water is contaminated a lot easier due to the small amount of water, and long shipping time.)
Drip i think is better, as you can control how fast the drips go pretty easily, and you dont have to worry about it quite as much. I also find that sometimes it can be hard to get bags to float well, even with creating and air pocket (maybe im just dumb though).
I have actually made a few big mistakes in cases where the bag is floating ok, i walk out of the room and i come back and the fish is swimming around in the water (knocked the bag over by himself, or the water flow of the tank did) The fish usually end up fine, in fact i have never lost a fish due to poor acclimation, but its still better to acclimate good obviously.
My vote went towards floating, cause i do that more often, but i would recommend drip method.
Jay
oh and by the way... sorry for rambling on so much lol.