I've personally used Kegconnection and ritebrew.com. Both have been awesome to deal with.
As far as pin lock (Coke products) vs. ball lock (Pepsi products), as was already mentioned, pin locks are a little cheaper, since they are more readily available. I like ball locks myself because of the physical size (taller and skinnier than pin locks, which fit better in my keg fridge), as well as the fact that they have a manual pressure release valve (convenient, but not necessary). A buddy of mine has a small store-purchased kegerator that doesn't have enough height clearance to accommodate a ball lock, so he uses a pin lock that was converted to ball lock, which is 3 inches shorter than an actual ball lock.
Before you decide which way to go, consider where you will be using them and figure out if size will be an issue. IIRC, ball locks are 8.5 dia x 25 tall and pin locks are 9.0 x 22. Also keep in mind that pin locks can be converted to ball lock and you can purchase ones that have already been converted. Cornykeg.com, among others, sells these.
I have 10 kegs and all were purchased used and had no problems cleaning them up. New would be nice, but I can't yet justify the cost when used ones work perfectly fine for about half the cost of new.
. You'll save a ton of money, won't care if they accidentally get dinged, won't feel like you always need to be cleaning them, and they'll function everybit as good as a new keg.
