I'd give good odds to the Druid (animal companion, spells), anyone who took the Wild Cohort feat, Fell Drain Sonic Snapping Wizards and Sorcerers (more so in a series of 1v1 matches than a free-for-all where they may be seen as the biggest threat and ganged up upon), Clerics (armor + domain bonuses + spells), Warmages (Warmage's Edge is actually pretty strong at level 1), and the DFA (Entangling Exhalation, I guess, although the average luck with that always seems to be pretty poor in practice for no apparent reason). Since it's a big FFA, there's a lot of both luck (especially at level 1) and metagaming involved (who to team up with/against). The strongest challenger won't necessarily win.