up until black and white i used to always take Tyranitar. now it will be Hydreigon (and yes i like dragon types. Hydreigon is the best dragon and dark type. unlike most of them he only has no 4x weakness which is why he is better than Tyranitar and Dragonite. they both are weaker than Hydreigon.
My new team as follows:
ive restarted in both versions 5x it least and my black version currently has lvl100 pokemon (but they aren't what i'd call strong except Hydreigon.)
i don't use legendaries btw for one reason they are overpowered completely and totally.