Well, the one that's always going to be special is the one you grew up with. This was MY theme.
I wasn't keen when it went all boingy and electronic in the 80s. Mind you, I liked the bit where Sylvester McCoy grinned and the melodic bit in the middle:
I was ok with the Eccleston and Tennant titles, but it was the Matt Smith ones in 2010 that really felt like proper Who.
And what of the new ones? Well, all very good, especially with that snippet of the Doctor's face, except they make me motion sick.
I also liked the first five episodes of series 7 having slightly different titles. I'm going to go with the 2010 Matt Smith original titles.