Personally, I like to use GHS Boomers (the red package) for electric (9-42, but I want to switch to 10-whatever).

For acoustic, I prefer Elixirs, (11-53, i think). They have a nice warm sound that lasts for a really long time. Although they aren't really bright, most strings that sound nice and bright fade after a couple of intense strum sessions, whereas Elixirs maintain their tone for months (at least for me they do).

One type of string I want to try is flatwound... I bought a pack, but I had just restrung my guitar.... I can't wait to try them!