Dick Sargent is often dismissed as the 'other' Darrin, and his episodes aren't as fondly remembered, because the show was in its waning years. However, Sargent did a good job portraying the character, adding an even more sardonic sense of humor.
It's worth noting that Sargent was the second choice to play Darrin when the show premeired, and since he was 'Plan B' in case York had been unavailable, he was the first guy they asked when York had to leave.
If I had to pick a favorite Darrin, I'd say York, just because he had better chemistry with Elizabeth Montgomery(by the early '70s, she was distracted by personal issues, and ready to move on, which affected the quality of the series.) Additionally, the replacement of York led to a lot of rewritten/rehashed story ideas over the last few seasons, turning 'Bewitched' into a pale imitation of itself.