On compilation albums that weren't carefully mastered for consistent loudness, I prefer to encode each song to the average of track gain and album gain. This assumes there is some validity to track gain, and some validity to album gain, and the average is the simplest compromise.
FB2k has the option of applying album gain or track gain, but no way to average them unless I manually alter the gain of each track and then apply that while encoding. This isn't terribly time-consuming, but it would be convenient if there's a way to apply the average of gain values, perhaps using a commandline approach (I'd be doing commandline-through-frontend, but that doesn't change anything as long as I can enter the command correctly).
I considered posting this in the FB2k hosted forum, but apart from some weird manual switch setting (that I don't believe exists in the FB2k interface), this seems more like a general audio question.