my favorite would be the byakugan,because it allows you to see at a bigger angle and you can see chakra points this makes the gental fist useable.(you do not have to have the byakugan to use the 8 trigram roatation,only chakra).
My favourite is the Sharingan because it can copy jutsu's as well as many other things but the main reason I like it is because of the Mangekyo Sharingan and the abilities it grants to the user Amaterasu and my favourite jutsu Tsukuyomi
sharingan and the byakugan cuz both are really cool. and both have advatigies and stuff the other one does not have.
My favorite Kekkei Genkai is the Bone one that that one guy had in the late naruto episodes it was so B.A.
hands down....sharingan. dead bone kimmi pulse is just too creepy. honestly, just think what you would do if you saw someone walking around in the mall with bones comming out of them