It’s kind of crazy for me to write a review of boats I haven’t paddled but hey, this is the Internet, so why not?
If your “to do” list includes tandem overnight trips, I’d avoid the 14’ models – they will be overloaded with two folks plus camping gear.
I have not paddled the Two Brothers canoes, but just looking at one on the top of someone’s truck I was favorably impressed. The lines looked good, the fit-and-finish looked good, to be blunt, better than the Buffalo canoes which I generally like as a reasonably priced, “do it all” canoe. So I would put those two above the Buffalo Canoes in your list. Between the two models – depends on what you want. My observations would be that the Arkota would be far better when tandem or paddling with a big load of camping gear due to it’s size; and probably faster due to its length. The big plus for the Brightwater would be that at 60# it will be noticeably easier to lift and move around than the 73# Arkota.
The Wenonah Prospector 15' will probably be the fastest of the boats you mentioned, making it a pleasure through pools, but a little less oriented towards whitewater. It will be fine on things like the Buffalo, maybe better than the other boats because the Buffalo has some long pools. Weight is also reasonable at 59#.
The Mad River Legend 15' seems to be designed for exactly what you have in mind. Compared to the Prospector, it weighs only 7# more; it will be a little slower in the pools, but a little better boat in the rapids. Neither of these two will haul the same amount of gear as the Arkota, but again all three are good boats, depending on whether you want to lean towards optimizing for gear capability, cruising the pools, or running the rapids.
Old Town Discovery 158 is heavy at 80#; you’ll notice that every time you load it. I don’t see any hull characteristic that is outstanding enough to offset this; if you can afford it and find one, get one of the other boats you mentioned.
Old Town Camper 15' – specs look good; haven’t had the chance to paddle one. Probably similar to the Wenonah. It may be almost identical, but if I had to gamble without the chance for a test paddle I’d go with the Wenonah simply because I’ve developed some brand loyalty growing out of the fact that I’ve never paddled a Wenonah that was a dog.
Old Town Guide – you didn’t say which length, but my answer is the same for both: Polyethylene boats are tough but HEAVY. Try to find one of the other models you listed that is a royalex boat. This speaks to why I’m not a huge fan of Old Town canoes, even though my dad was because the company existed since 1898: the company has a mix of really decent boats, and boats intended for the “entry level” market. Some companies just don’t make any bad boats; but Old Town has a mix of good boats and cheaper, heavier models I wouldn’t want, so you have to pay close attention to what model you’re looking at.
SO, to summarize: Avoid the poly boats (Discovery, Guide). For the rivers you describe; go with the Legend for best whitewater performance; the Wenonah or Camper for best performance in the flats, or the Arkota for mid-range performance with monster gear hauling capability. I’d also suggest looking at the reviews and ratings you find on paddling.net – If you read between the lines and look for those 8/10 and higher ratings, you can figure out which models folks are really excited about owning, and which ones think their boat is just “OK”.
These are just my thoughts; I’m hoping some others will chime in too because I’d like to hear more opinions.