Hi bsartin,
my personal favourite species due to being stunningly beautiful, CLEARLY intelligent, personality wise, responsiveness etc, etc, is V. salvator.....
Then again, it`s also V. varius, V. bengalensis, V. niloticus, V. ornatus, etc...
I cannot choose between them, because ALL the species I`ve kept have those characteristics, and I`ve been fortunate to have (over time) very tractable individuals, which makes the whole experience so much more rewarding, in my opinion!