You need a 'Deep Cycle' battery for a trolling motor. If the TM is the only significant piece of equipment you'll have hooked up to the battery (ie no electric start gas motor), get a true deep cycle. Deep cycles will give you a longer draw, and can handle multiple recharges from an 80% drain without needing to be replaced in short order. Complete drain downs can be handled, but you never really want to run any battery down to 0% if you want it to last. Deep cycles have thicker solid plates, which allows for this. You should be ok with a hybrid/marine battery, which is a cross between a deep cycle and a starting battery.
As for brand, they say you get what you pay for, and I get WalMart. :mrgreen: Get a WalMart (EverMaxx is the brand name I think), and see how it does for you.