Spitter is VERY useful in Versus. The survivors can't see the spit coming (though you usually hear one of them go "Spit incoming!". A good spit can easily incap low health survivors, or do 50+ damage to everyone, even if they react immediately to get out of it.
Charger is not very powerful. His health is low (not as low as the spitter's) and so he can be killed pretty easily. Unless you can either a) pick off a straggler or b) carry a survivor far enough away that it takes them a bit to catch up you'll die before doing any real damage.
Of course in conjunction with other attacks from other infected a Charger can prove to also be quite a distraction.
Jockeys can guide players off ledges so they have to hang and get someone to pull them up (but the Jockey immediately goes over the ledge... lame :().
Recently I was playing Versus and got to be the tank in a small area with dumpsters and cars to fling around. Good times, easy incaps.
I am not very good at Versus otherwise though. I keep trying to hunter-pounce or charge or jockey pounce survivors near a ledge to try and knock them off but I end up just running off and making them laugh.
I tried Scavenger and my team got soundly beaten. Well I assume we did, my computer BSoDed right before the survivors got their last tank of gas. It was fun though, Spitter is very useful there as well since she can explode dropped gas cans, which is especially useful on the mall level. A good tactic on that level is for the survivors to split up... the dev commentary mentions that this is sometimes a strategy they try to get you to do but it's never mandatory... and have two guys go to the third floor, drop all the cans down, and then drop down through a glass floor to the second floor and get all the cans there and drop them over the edge. Whoever is on the ground floor handles filling the tank. This is where the Spitter can come in, she can spit on the gas tank to seriously hurt any survivors hanging around it, as well as spit the dropped gas cans to explode them.