I didn't A/B tried C3 against ReaXcomp, but some years ago, i was prefering Buzroom Grancomp3 over the C3, which is also free. Nowadays, i tend to use ReaXcomp, or JB Broadcast, which is 3band, free, and has some nice mid/side processing features. (One thing, fyi, the FL multiband compressor is the sss C3 with new clothes).