Hello all, this is a first time post, but I decided to throw in my two cents this time instead of just lurking around the boards. (Like I have for the past week or two.) Have to say it's a wonderful community, with plenty of knowledge to go around. Anyways, a few points. . .
Gotta be a channeler. It would be cool to be a mistborn, but you can only do so much with allomancy. You can do ANYTHING with the one power if you can find the right weave. Besides, it'd be easy for a channeler to kick a mistborn's trash. Just hold him still with air and balefire the heck out of him/her.
It might not quite be that easy for a channeler to fight a Mistborn though, especially if said Mistborn was either really rich, or had abilities such as feruchemy and hemalurgy to supplement their allomancy.
For example, if the Mistborn had a large enough cache of atium and other metals at their disposal, then I'd have to give them the edge in any fight. Being able to see what your opponent is going to do before they do it is something no Aes Sedai or Asha'man could counter, and you could probably tell at least if the channeler was going to balefire you via some combination of gold, electrum, and atium. (Though that makes me wonder if gold, electrum, and malatium shadows throw off an atium shadow if you burn both. Hmm.)
Or supposing the Mistborn had feruchemy and hemalurgy to increase their abilities, (like the Lord Ruler,) then they could burn a whopping load of speed and wakefulness, in addition to atium, to create a body that is fast enough to take out the opposing channeler before they have a chance to react. Or supposing they were
really powerful, they could just use a huge steelpush to separate each individual molecule in an opposing force, by pushing on the iron in their blood and tissues. (Messy way to go though. Ick.)
I guess in the end it mostly comes down to surprise. Either the channeler is going to get a net of air around the Mistborn, or the Mistborn (if they're competent or lucky enough) is going to get to the channeler before they can react.
But back to the topic at hand, I would probably go with a Mistborn. While it's true Aes Sedai and Asha'man can do a much larger range of things, and would probably be a more versatile and worthwhile choice, Mistborn just strike me as more, well, striking. And Mistborn can do several things channelers can't, such as burn temporal metals and "fly."
Well, I think that's all I've got for now, but hopefully I'll think of some good content to add to the other discussions as well.