Well, let me give my thoughts...

The Weapons Of Choice:

Most powerful weapon combo depends on the map and my particular mood:

M4/Kevlar in 3-burst mode is very effective for open maps like Urban1 or 2 and TeamJungle. This combo is pretty accurate and gives you durability against other lead spammers. You must stop to shoot if you plan to hit with regularity. If running or walking, you will get bullet scatter. If you do not 3-burst, it will really scatter.

M4/Laser is very accurate and quite a bit of stopping power. You are less protected and must be stealthy and quick. You can run and jump and expect to hit fairly regularly in 3-burst mode. In full auto you will have to spam quite a bit of lead to get a killing hit, while moving. Someone that stands still and has good aim will most likely take you
out.

MP5/Laser is probably the most accurate weapon while either running or stopped. It has less stopping power than M4. So, a headshot with it still might leave a good player with a chance to take you down with
their weapon. He will die, but you might die too. I like this combo if there is a lot of ground-level strafe shooting.

MP5/Silencer is good only in close and dark maps. I like to stand in the shadows and 3-burst people that go running by. They rarely know what has hit them. The unfortunate part is that it is not very accurate and they may get away merely wounded. Headshots are hard with it. A
side benefit is that the pistol is also silenced when you run out of ammo for the machine gun. The pistol in semi-auto mode is quite accurate and deadly.

The pump shotgun and akimbo pistols are both of similar effectiveness in my hands. I have seen some shotgunners that are very good. They just kinda whittle you down to nothing from a medium distance and good cover. Very annoying! The akimbo pistols are good for close range lead spamming. If at a distance, I would drop to single pistol, semi-auto,
and crouch.

The knives have a real cult following. They are not the hardest to get good with, but they are frustrating. They move fairly slowly. However, they are the only projectile that will arc and hit a target out of direct line of sight. (Can you say, "Surprise!!"?) They will penetrate Kevlar and are a sure kill when you hit the head. I am not good with them. However, I have seen good LPB knifers that would lead the tote board... not just their team. They can be very frightening. Especially if they wear the "Bunny Slippers" aka Stealth Slippers. For instance, I might be bopping along all happy and healthy, coming to a corner, then the next thing I hear is a sickening "sploosh" as I catch a knife with my forehead. "Doh!" You just don't hear anything.... which reminds me...

The sniper rifle with the silencer is one scary weapon in the hands of a master. I watched one guy dismantle my entire team of 4 or 5 of us. He takes me out first, "crud", then I watch him. He just moves around the
map, positions guys into pinch points, then "psssttt", pops them. With the silencer it can be like death from "no-where". Very intense! Some guys will sniper rifle with Kevlar. They are more durable, but they
become visible via muzzle flash and audible via report. They still may nail you, but you generally know about where they are.

I have used the sniper rifle with good effectiveness. However, I have to be on ping parity with my victims... or lucky or they have to be lamers. I can take out guys from hiding pretty well. However, I am not good enough to take on a machine gun or pistol packing guy in an open street. Some snipers are that good!

The Handcannon can be fearsome. I have had some of my most hilarious Kodak Moments with it. However, it is, in my hands, only good for close maps. Ones where the long range lead spammers cannot draw a decent bead on you. Launching an enemy into the air when he is either just above you or you are crouched is one of the most hilarious sights for you. It is probably one of the most fearsome sights for the enemy team as the poor b*st*rd gets launched with a crimson geyser spouting and his gear all flopping away from him. Yehaa!

The Binds I Regularly Use

Presuming a primary QWES movement mapping... (these are not the actual commands, look in the readme for them!)
bind 1 weapon (knife changes from slash to throw. Autos change from
auto to 3-burst. Sniper rifle goes to scope mode, etc.)
bind 2 single pistol
bind 3 akimbo pistol
bind 4 knives
bind F2 Team Report In!
bind F3 Reporting In!
bind a Enemy Spotted
bind d Enemy Down
bind PgUp "Up" (the voice command)
bind PgDn "Down" (voice)
bind y "Right!" (voice... I use it as a synonym for "affirmative" to
another teammates message.)
bind r Special (your special weapon)
bind c crouch
bind z drop item
bind x drop special
bind v open door
bind b bandage
bind g messagemode2 or team_say
bind mouse2 reload

Using Cover

Hey! This is war! When you do that CTF/DM "Charge of the Light Brigade" you are usually gonna die. Boxes, trees, walls, bunkers,
corners, and rocks are all your friends. Learn to keep them in between you and your foe. Also, learn to crouch down, strafe, shoot, strafe back behind your cover. If you hear running and you are near cover, duck into it and listen/watch. You may be able to ambush someone that is running, less accurate, and likely to be surprised by your initial burst. Also, I usually wait for the initial charge of the newbies and youngsters. They will sometimes spam an entire clip at a team off in the distance. I will wait until they stop, then come out with my bursted fire. Sometimes I catch them reloading or bandaging.

As in any Q2 or Q1 game, knowing the map is crucial. As you also know, that just takes time. It helped me to load up a local game on my machine and just run and jump around the maps. I even started firing at the walls to see how my bullets were hitting while
walking/running/crouching/standing. Nerdy, sure.... 8-P

Good luck and cya out there!