Both are excellent games, and some of the best value-for-money titles available right now. I couldn't pick between the two overall. As was noted by EchoVictor, Doctor Who is a lot like Pinbot in some regards. Judge Dredd isn't really like anything else that I've played
Judge Dredd is commonly referred to as a $1400 game; that's a bit lower than the average, but the majority of sales fall in the range of $1300-1800. I'd say $1600 is about right for the game at this point. With patience, you may find one for less; I did.
My knowledge of Doctor Who prices isn't as good, but I'd say $1800, roughly.
I own a Judge Dredd, and a friend nearby has a Doctor Who. I've played both a fair bit, and think both are easily worth the going rate.