the reg is fine.
the best NA pubs are the KKG's, add them as a bookmark. better players tend to play there.
skulk is awful. marines move faster jumping backwards than you do jumping forward. gorge is pretty fun if you can land your shots, untouchable if you have a good gorge partner. lerk is the bird that flys around. you gain speed by flapping your wings a couple times (space bar). against good players, never rush them to bite if they know you're there, you only bite when they aren't looking at you. use your spikes to harass. fade has the highest skill ceiling. ideally you want to get good at fade with just shadowstep (not blink), because a lot of the time in both pub/comp you don't get blink until later on. do not rush more than 1 shotgunner without carapace, even then it's risky if they're decent.
as commander, if someone asks for ammo/medpack/mist, press spacebar and it takes you to them.
combat mode isn't terrible; think of it as NS2's SOAP DM. you level up based on kills/assist and can purchase upgrades with your levels. don't take it as serious as the random gays in it that get mad if you lose; marines rarely win.
edit:
skulk: adrenaline(if you have leap, celerity otherwise) / silence / carapace
gorge: adrenaline(although celerity is pretty hilarious) / silence / carapace
lerk: celerity / silence / carapace or regen depending on playstyle
fade: adrenaline / silence / carapace
onos: either or / silence / carapace