If you search around you can find a number of comparisons of the tools. They have different information in them so it will really depend on things like what airline you are flying/researching and what actual details you are looking for. Neither of the two is just plain "better" than the other. Both rely on other services for their data so the update and whatnot should happen at the same time in theory, though, again, it depends on what exactly you are looking for.

Here are two of the more recent/coherent threads comparing the tools for some reference:
http://www.flyertalk.com/forum/trave...vs+expertflyer
http://www.flyertalk.com/forum/trave...vs+expertflyer

I'm going to lock this thread and suggest that you continue the discussion in one of the other threads if there are questions that aren't answered in them.