Achievements are ubiquitous at this point, from World of Warcraft to Warhammer Online (and that's just the Ws). Despite usually not offering anything more substantial than a pat on the back and a few numbers for your number collections, they have proved to be an incredibly popular motivator to going outside of your daily routine.
Collections are somewhat more tangible: in-game objects that are often hidden for you to seek out, find, and collect all of them for the cool prize on the back of the box. That may be Cheerios, too. Anyway, titles like EverQuest II and RIFT enjoy sending players out on these scavenger hunts, and it momentarily takes our minds off the presence of death and slaughter that permeates everything.
So if you had to pick one of these systems as the better motivation to get you out of your comfort zone and try new things, which would it be: achievements or collections?