I used SVN with a centralized repository for a while. Horrible. The local repository got huge, even with the SmartSVN user interface it was confusing and every other day there were some conflicts that would prevent me from checking in and out and I had to going through confusing options to get it all going.
I am now using Perforce and it is a blessing! It’s free for up to 5 users and there are absolutely NO problems. I love it and if I worked in a larger company I would lobby hard for a purchase. Forget all this open source stuff. Perforce is superbly integrated with UE, there’s a plugin for the Visual Studio IDE and a free stand alone graphical interface. I believe Epic are also using Perforce.