In a short 1v1, Feruchemist beats Allomancer easily. In an exteded fight however, or against multiple opponents, Feruchemy begins to suffer. It's good for quick, focused bursts.
In a longer, more extended battle, Allomancy wins, as it has no real limitations to how long it keeps going. Add pewter to the mix, and I find that allomancers are built to fight for very long stretches of time.
Unfortunately for us all, Hemalurgy is both abilities, and more. If, for any reason, you figured out where to stick the spikes, and then managed to kill even one person, you would gain the powers of a ferring or misting. Using those powers, you could kill another person, therefore doubling your power. If you played it safe, you could become rediculously powerful. Supposedly mental fortitude makes you insane, but in the event that you found a way to beat it, it could be used to counter bodily take-over if you had enough of it.
All in all, I think Hemalurgy is the superior art if you're clever with it. Neglecting that, in short fights, Feruchemy wins. In long fights, Allomancy takes the cake (Provided GLaDOS isn't nearby).