Isn't MFR BioGen more efective?
Tree farm is easier. It is just 1 kind of farm. For making Biofuel, it would be better if you could manage at least 5~6 different kinds of farm so the efficiency is better.
Say, the most common type of plantable crops would be wheat, carrot and potato? Melon and Pumpkin with some autocrafting processors to get the seeds out of them? Netherwarts can be farmed and fed to the bioreactor as well. So that is 6 kinds, if you get at least 3 different kind of tree farms, that will bring the numbers up to 9.
But if you have to have a tree farm anyway, why not just use the steam boilers? I mean, my 9 x 9 oak tree farm produces more than enough wood to process into charcoal to feed at least 2 steam boilers (it should be able to provide for more than just 2, I just have not tested the limits yet). That supports 18 steam dynamo (1440 RF/t) or 18 Industrial Steam Engines (144 MJ/t). Those charcoal can be used to fuel IC2 too (I guess? I've stopped playing with IC2/GT after 1.4.7).
tl;dr version
I find that a single tree farm is a lot easier, compared to making biofuel efficiently.