They're both very well done games, but I'm more into Sonny type games, so I'd have to go with Sonny, although, I did absolutely love every second of the first Last Stand, and loved the 2nd one twice as much!
Its hard to compare the two because to me they are two different styles of game, Therefore I can't choose one over the other based on the fact that each one does things better than the other and some thins that the other cannot do entirely.