Yeah I upgraded some, and I unlocked some. I definitely think it's best to check it out before hand. Since there's some upgrades that you need to have on any gun you run, you probably can't afford to run at a higher gun tier with upgrades all the time. Pick a few guns in the list you like and get your upgrades then rush to the next one.
Some guns are very specialised which is fine if you run that role or build a lot, but it's better to stick with general purpose guns.
I've been running recon with scanner/smg, I run with the supports for offensive scans. Cloak/smg is good for breaking through, but I don't like to run it all the time since it has less utility. Cloak/sniper is obviously the best in the world for kills, but whatever you don't win the game by getting kills!
I want to run support but I don't have the ping for it. If I can get a fireteam I can run it but pubs don't have the communications :/