I use lipos. They hold a charge for a much longer time, work much more efficiently, and are lighter than nixx batteries. It's just so much easier than trying to keep all your batteries ready for flight at any given point.

If you really don't want to get involved with lipos, then I follow Mr. Greybeard's school of thought - slow charge when I get home, but fast charge the am I want to fly, or in the car on the way to the field. Batteries are cheap enough for me to use them in a convenient way, and spending hours of my valuable time on a $15.00 battery is just asinine.