If you're watching the old ones - from 1963 to 1989ish - you most likely won't like them until you get into it and know what you're doing. I'm on the 4th Doctor now, and I am LOVING it, and he's now my favorite doctor. But if I had tried to start there, I never would have been able to get into it.
If you're watching the first of the new ones from 2005, that's the 9th Doctor. I liked him, but there are tons of people that don't. There is a new Doctor, the 10th Doctor, the following season, so you could start there. It's also super easy to start with the 11th Doctor in season 5 of the new ones. And if all else fails, I like to start people off with "Doctor Who: A Christmas Carol" because it's super fun and it's the episode that made me actually like the 11th Doctor (I really didn't want to see 10 go
but I'm over it and 11 really is great).
You could actually start anywhere, but those are the best starting points.