I tune standard. I seem to not have a problem with songs because of the key. But I think the advantage comes purely from your style of play. If you use a lot of open strings, harmonics, etc, then for flat keys you get a benefit of tuning flat. I've heard of some folks carrying 2 basses, one tuned flat and one tuned standard, so regardless of the key, they're ready with the suitable tuning.
Its all a preference. Examine how you play, explore it if you think it may make a difference. If it does, no big deal. If it doesnt, no big deal. Its all about what you want and what works for you. Just dont get into the school of thinking that "it has to be done this way or this way is better because ***insert popular well know bass player here*** does it this way"