I go for achievements that are feasible. Many games have achievements that are all easily doable - they may take time to do, but they're doable, and overall, not that difficult. Games like Mass Effect, Fallout 3, Assassin's Creed.
Other games have ridiculous requirements for their achievements, like Blue Dragon.
I'm not going to stress myself over achievements that would just stress me out.
I also don't go for Online achievements.