Those twin trunks with fluting are really nice. Can't tell the exact scale, they look BIG, but not too big to get--if you want to pay for a very very large bonsai pot down the road. In any case, those are the kinds of tree you should be looking for. Don't get caught up in mistaking weird looking as preferable. Bonsai should look natural not odd. Those twin trunks have fluting and pretty nice dramatic taper from the roots up. keep that in mind.
The fluted trunk with the knees is nice, but the knees are mostly useless for a "final" bonsai image as they're waaay out of scale. The trunk, however, can be collected without the knees.
BTW, you should be looking for cedar elm as well. They are everywhere in that area. They are EXCELLENT bonsai material and if dug in the right season (early spring just before bud break--like late Feb. early March), they are extremely easy to collect with a cordless handheld sawzall reciprocating saw -- you don't need much, if any feeder roots with them.