The Survivors are tough, hardened, and know how to keep alive. They have high health, but are low in numbers; and their weapons are not particularly phenomenal.
They will have to scavenge to get better gear from the Bandits and Military. Their vehicle is a pickup truck with a few seats for passengers. For Bandits and Military, it is worth hunting Survivors due to their high loot-drop rate, and they also get Impact Pipe Bombs which (needless to say) are much better than Grenades when facing Infected. They are the only faction that can become wounded and actually utilize the medical kits.

The Bandits are well-equipped, and they have good numbers. They may not have as thick a skin as Survivors, but they pack some of the meanest gear around; ranging from AKs to full-auto Glocks, Desert Eagles, and the devastating AA-12. Their vehicle is a pickup with a mounted .50cal MG, and sometimes an AI-controlled 'Bandit Grenadier' will spawn with an MGL-140 Grenade Launcher or an AA-12 with Frag rounds.

The Military have the best gear available, and are the most prepared to hold off the Hordes of the Infected. However, as a Survivor or Bandit, you'll be out to get these guys for their gear. With large numbers of M16s and other automatics, they can also purchase Light MGs, the Barrett M107, and the M134 Minigun. At a high enough rank, they can call in a Jet Airstrike to blow sh*t up. They also get two vehicles; the Jeep and the Humvee.

The Infected are extremely numerous, attacking in massive groups and mindlessly charging their targets. They tend to have fairly high health, and come in a large variety of shapes and sizes. There are a few categories of Infected:

-Normal ol' Walker - Medium health and normal run speed. Best dealt with Semi or Automatic weapons. Their exact health and speed vary from zombie to zombie.
-"Very recently Infected" - extremely low health, but very fast run speed. Any weapon will deal with these guys, but you don't want to be caught prone reloading your LMG with them guys charging you. 9mm Pistols are your friend here.
-Brute - high health and a bit slow. Not a huge threat if you're toting an Automatic.
-Riot Brute - higher health than the regular Brute, same speed. These guys absorb a fair amount of punishment before going down.
-Bloated - extremely high health but very, very slow. Basically a bullet sponge - they are a nuisance to deal with when facing them combined with a Horde.
-"Unstoppable" - extremely high health and normal speed. These guys are the biggest threat around, but they're fairly rare to encounter. You'll need a lot of Automatic fire, or a few rounds of .50 cal to take this hulking mass of flesh down.