The lights are on
Med Kit or Defib? The decision can sometimes be tough, but it really depends on what situation. I've been playing L4D for a long time and in Versus, I'd pick the defib. Make sure your teammates are watching your back because three survivors is much different than four. You could always use the extra hand, right?. The situation NOT to pick it is when you all have low health. But then again, you could just heal and pick the defib back up, couldn't you?
Adrenaline or Pills? Pills. Although adrenaline is quick acting and improves skills, its use is so short. Think about. When running from a tank, what will last longer: pills! The only situation that is the exception is when you must shut off an alarm far away. You need speed for such an occasion.
Boomer Bile, Molotov, or Pipe-bomb? Here are the reasons why a molotov is the better choice (except in Scavenge).
A pipe-bomb is just a really short distraction for the horde. I've had plenty of times when only about 5 or 6 common infected have made it to the explosion and the horde just turned right around and attacked again. Plus, the zombies that bump into you on their way to the pipebomb stop, punch, and slow you down. The pipe-bombs also have no affect on Special Infected.
A boomer bile jar is used for fun time. Throw it down, go ahead. Watch the common infected swarm the area while you leave them in the dust. Well, in several seconds, you'll not only be dealing with the foes in front, but also ones from behind that you DIDN'T kill. Yeah! Zombie flanking! Also, throwing a bile bomb at a witch won't help unless she's around common infected. She sprints faster than they can run or even appear off-screen. The only time throwing one at a tank is worth something is when you don't have the achievement Septic Tank. It has too much power and will be slowed down and wounded a little bit. Plus, the infected that you summoned will turn against you when the slime goes away. This will make the tank's job easier.
The molotov's only weakness is it's uselessness against Uncommon common in The Parish. It keeps burning on any Special Infected until they're dead and is an instant kill on any common infected (except Hazmat suit). It slows down the witch's sprint, takes significant damage from the tank, and gives you an automatic area coverage. Just don't step too close!
Primary weapon choice depends on how you use it or what you're most comfortable with. My favorites are the SMG, M-16 Assault Rifle, Desert Rifle/SCAR, AK-47, Auto-Shotgun, and, of course, the amazing Grenade Launcher!
When the time comes to decide for a secondary weapon, ALWAYS choose the melee weapon. In L4D2, they put a melee shove cap on for a reason: you can have melee weapons! When the zombies are swarming you, double pistols can't rid you of their presence fast enough. A few quick fire-axe swings will do the trick, though.