Killebrew, no question. Home runs and power are a big part of the game, that's why I would never consider a player who can't hit a lot of homers "the greatest". Roberto Clemente was a heck of a player but only hit 240 home runs, if he hit 500+ maybe he'd be in the conversation.
What I really like about batting average is that it's power and body type neutral, strong players don't automatically have an advantage over weaker players. This is also why I like triples, doubles, and singles. All players are basically equal concerning these stats, all players can do well or not. Rod Carew was a great player, he had a BA of .328 but only hit 92 home runs. He could compete with Killebrew, Bonds, and everyone else in BA and did. The only chance he had in competing in homers was taking performance enhancing substances. Carew could never be in the conversation of "the greatest" because he wasn't strong enough.
This is my problem with Bonds, power/strength/muscles/drugs couldn't help him as much in these few categories and look what happened - 231st in BA (and not a .300 hitter), 303rd in triples, and 207th in singles (he did do well hitting doubles, he's 14th all-time). Mays and Ruth didn't do nearly as bad. I believe Mays is the only player in history that isn't outside the top 200 in any stat.
Bonds is definitely a better power hitter than Mays and probably Ruth, without the drugs he most probably isn't. If people want to call him the greatest of all-time that's fine with me, I'm just not going to give a .200+ hitter who can't make the top 200 in several stats that title.