I have them re-roll 1's and 2's until everything is at least a 3, plus I allow 4d6 for each stat, take the best 3 of the 4. So 15 is the average/most common stat for PC's (and key NPC's) in my games.
As for HP's I use a graduated re-roll system.
d4 classes re-roll 1's until a 2 or better is rolled.
d6 and d8 classes re-roll on 1's and 2's until 3 or better is rolled
d10 classes re-roll 1-3's until a 4 or better is rolled.
d12 classes re-roll 1-4's until a 5 or better is rolled.
There are no whimpy PC's, or key bad guys, in my games.