I prefer about 80% to come from goals (which usually means treasure, but if the DM has designed an adventure in which the goal isn't to gain treasure, he should also modify the XP rewards appropriately -- or at least not wonder why the players are more interested in gathering treasure than accomplishing their ostensible goal...). Combat is, for me, one of the least fun parts of the game, so I really don't like XP-rewarding schemes that expect/force me to spend a lot of time in combat and especially ones that punish rather than reward me for successfully avoiding it.