my 2c on NRS frames/packages
i have an older 11.5' NRS otter that i fish from with the basic NRS fishing frame (only one person fishing in front). i also have a 15' NRS otter with the full NRS fishing frame (two people fishing, one elevated seat in front and one seat on the stern).
i chose the NRS frames so that i could have maximum flexibility for different uses. i also row both boats for whitewater and overnight trips, so i can easily take the fishing seats off to rig the frame with a cooler, dry box, seat board, etc. the ability to reconfigure other frames such as DRE and AAA is both limited and cumbersome IMO, and the outcast frames cannot be modified at all. i have acquired a few extra cross bars for my frames, so i can just take the fishing seats off and put the straight cross bars in for whitewater with a cooler of beer. or i can leave the front seat on the big raft, and create some gear bays in the middle and stern of the boat to be rigged for a multi-day fishing trip.
my neighbor also has the 14' NRS Otter fishing package (included raft, frame, oars, lean bars, casting floors, etc) that he purchased in 2010, so i have fished on that several times. i don't find the casting floors and lean bars to be of much use for the type of water i like to fish in colorado, but that is admittedly my personal choice. if i were fishing slower water with very few rapids (like sections A/B/C of the green for example) more regularly, a casting floor may have more appeal to me. one thing to note here is that my neighbor sold a 16' cat with a NRS fishing frame set up (only one fishing seat up front) to buy his 14' raft package. he said he wanted the additional flexibility the raft would offer and he felt safer taking his kids in the raft instead of the cat.
if i were to only have one raft for fishing, i would choose a 13'. i think a 13' raft is large enough to comfortably fish with two people (one in front and one in back), but still agile and small enough to take out when the water gets a little low. my 11.5' raft is packed full for a day trip with just one person fishing, and it would be very tight (basically impossible) to put a stern seat on that set up. having fished and rowed my neighbors 14', i find it a little too big when the water starts getting low. it is also difficult to move around and get on the trailer if there are only two of us.
given all of this, a 13' raft would be an ideal size for fishing colorado IMO. if i could only have one, i would choose the 13' NRS fishing package and get a couple extra cross bars to give me the flexibility to rig for whitewater and booze cruises. i would also get the NRS anchor system added to the package, it is a great addition for the money. this is all based on my personal preferences, experiences, and the water i like to fish, so i certainly respect the opinions and preferences that other folks have expressed here. the bottom line is that whatever craft and frame you choose you will be able to enjoy some great fishing.