World Community Grid is more of a platform, where you can choose to run different projects: proteion folding (similar to Folding@home) is one of those. There are manu more: Computing for clean water, fight childhood cancer, cure muscular dystrophy, fight AIDS@home, discovering dengue drugs and so on. These projects differ much more - they cover environmental issues, epidemiology, biochemistry, microbiology.
Folding@home is more of a method: calculating how to fold different proteins so they are stable and use the least energy. Folding@home has also different projetcs, but these projects are all about folding different proteins ... and the benefit is much more basic science than the projects in WCG.
Both are very worthy projects (I for myself contribute to both and I am the captain of the WCG-team: TeAm Anandtech). I think it is rather your hardware and your knowledge of computers which may decide which project to join.
WCG is miuch simpler: set up BOINC, select WCG for your project and crunch away.
F@H meeds somewhat more of knowledge about your hardware to decide which clients (=calculation programs) to run on which CPU, if you have powerful graphics cards, which GPU-client to use, how to set them up, etc. It is not hard (most can learn that from the forum in 10 - 15 minutes) but then there may be more of a hustle of upgrading the clients for optimal computing and then there are the races and competions - much more in F@H than in WCG.
My point is: read more, learn about how to optimally use your hardware and choose or/and try what suits you best.