I agree with the last two posters. I think its a lot more useful to talk about classes in "# of average hits till unconscious", when talking about starting HP.
I like the tensions to be around 'a wizard should take two hits. A fighter 3-4'.
If monsters are dishing out hits at about 1d6 per round at the first level, that's 3.5 per round on average, so a wizard should be suitably frail with 7 hit points. That would be at a base level of CON 10. But if a monsters damage is going to be more than this on average, HPs should increase as well.
A fighter at 3.5 per hit should be at about 10.5 to 14 HP before con mods.
It all sort of depends on what they do with crits as well. People like extra damage on a crits because big number are exciting, but that's leads to a lot of problems. I'm not a huge fan of an orc being able to drop a wizard in one hit, however low the odds, but it should be very close...
Has anyone ever played around with crits causing temporary stat damage? Say a broken wrist or a concussions (loss of Int)? Horrible scars modifying char? Anyway, probably the wrong thread for this sort of thing... but I wonder if there's a fun mechanic that doesn't mean doubling damage dice.