I prefer Lock Stock. I dunno, it just seems a bit more "authentic". Snatch seems like it was assembled from the same "parts bin", using leftovers after Lock Stock was finished.
Both are great movies, mind you, and both have extremely memorable moments, but Lock Stock seems to come together alot better, and when someone says "Guy Ritchie", it is the movie that comes to mind first.
Not very scientific, but there you are.
EDIT: Well, this thread just inspired me to whip out my Lock Stock avatar. Way to go, people
