Though there are many projects in this category (see Simple GCC projects), I plan to focus on those which are geared towards improving code cleanliness in gcc. Specifically, I plan to begin with warning squelching, as that will not only be a project which will be well within my ability and in which there should be a lot to do, but also a project which will give me some familiarity with the gcc code, which will provide a good springboard for getting more involved
The principle advantage to working in GCC will be the extent of work that needs to be done, and the range of required experience required by that work. If I feel over or underwhelmed with what I start working on, I will have other good tasks within the same project that I can consider as alternatives.