There are pros and cons to each show. I watch both of them and like them both so I think I'm qualified to judge them.
True Blood is for a more mature audience with their sexual suggestions and other darker aspects but in my opinion it lacks a solid coherent plot. Each of the seasons have been pretty much stand alone seasons that don't have much of a connection with each other.
Vampire Diaries is more of a teenage audience but it has a nice solid story. Each season builds on each other and stresses more of the character relations. Like, if someone died in True Blood it would almost be expected, but if someone dies in Vampire Diaries it'd be a HUGE deal. I also like that VD has more episodes per season.
In terms of vampire representation, I HATE the vampires in True Blood. I hate how their fangs pop out like flippers and I hate how they explode into a pile of bloody crap when they die. The werewolves are disappointing too -_-
I love the vampires on Vampire Diaries though. How the veins around their eyes darken (kinda like a black Byakugan now that I think about it LOL) and when they die it isn't so over the top. I also like the whole vervain thing. And I like their representation of werewolves (nice and simple) and their witches