What guns for a beginner? Here's my humble opinion.
15awg 2.5" Finish Nailer- 34 degree angle. The angle lets it get in between stuff easier.
18awg 2" Brad nailer. (not a stapler combo) Don't mess with a 1.25" Brad nailer- thats what i have and would much rather have the capacity.
23awg 1.25" Headless Pinner.
If its not clear, the 2.5", 2", and 1.25" are maximum nails- you can use anything shorter in those guns.
Thats a perfect combination in my mind. the Pinner is really just a bonus. the first two will accomplish about any task.
For brand... the other suggestions are fine... but I got my brad nailer at Menards (Tool Shop brand) for $20. I've shot a couple thousand brads with it and haven't had a single jam or problem. only complaint is the size, but they have a 2" for $30. My Pinner is one of the blue ones from Harbor Freight- $25. only used it for a couple projects so far, but no complaints yet- especially when a Grex is $300... I don't have a 15awg nailer yet, but I'd prolly go for a Grizzly- like $110. my point is... this isn't a drill with a motor or a chuck, its not a saw... it's just a valve to hold back the air till you pull the trigger... not too much to go wrong. I'm all about top quality stuff where it matters- I use a Ridgid drill and Makita 10" SCMS, but in this case... Cheapo has worked for me so far. I'd sure be mad if I bought a $150 brad nailer and then wish it were 2". as it is, my experiment doesn't have me out much.
just my $.02