Holy Cow. That's like asking "what's the best flavor of ice cream." or "who makes the best truck." Lots of opinions. I'll put in my 2 cents and the reasons why. I like NRS. Not everyone does, but I do. Here's why......
#1 - I like to tinker with my frame. Move things around, reconfigure, mess with it. Make bays bigger or smaller to fit different coolers/boxes/gear/passengers, etc. I also like to pick & choose the parts I want. The NRS modular system lets me do all this.
#2 - I have limited storage space. I can take my frames apart and store them on shelves in my garage. Easy, light weight pieces to store.
#3 - I run with a group that often does late season, fly-in Middle Fork trips. My frame pieces fit easily in the plane. PITA to have to put it together at Indian Creek? Yes, kind of, but not that big of a deal.
#4 - The NRS frame shop & customer service folks have always been knowledgable, friendly, and they will make custom stuff if I need it.
#5 - Cheapest choice - no, lightest choice - no. Best choice - ??? But when I order a part, I know exactly what I'm getting. All their frame part specs are on the website, so no surprises. I know friends who have spent countless hours in phone calls and e-mails back and forth with out of state frame builders to work out all the details of a frame, only to have it delivered and be wrong.
If you are lucky enough to live close to a frame builder, then that's great. You can look at their stuff, talk design, and get a nice frame that suits your needs.
For what it's worth. I'm outfitting a new raft and got a basic NRS Compact Outfitter frame (custom sizing and I already have the oar towers) for $460. Nothing fancy, but I can pimp it out whenever I want (and have the $$$).
Good luck with your frame. And remember..... it's just the means to get you out on the river. Don't stress over it too much and miss the point of this crazy hobby/obsession