What does generally sound better (more transparent): AAC LC (Low Complexity) or MP3 (VBR, quality level V -2)? Thanks.

Lame -V 2 is transparent on nearly everything. For which encoder and what settings are you asking about LC AAC?

I'm asking about AAC LC encoding using FAAC (with BonkEnc) as well as MP3 VBR (V -2) encoded with LAME 3.97 (with BonkEnc). Thanks.

nero aac is better than faac. it's just as free, too.

Both Nero AAC and iTunes AAC would be better encoders than FAAC as, to my knowledge, it hasn't been updated in quite a bit of time and it never posed any benefit when it was originally released oh so long ago.

I suggest that you look at some of the past listening tests here on HA as they will show that the 128kbps VBR bitrate is actually quite transparent. At the -V 2 range, the differences between the AAC and mp3 format are slim to none except with Lame killer samples (though each AAC encoder has their own killer samples as well). Try encoding a couple of tracks to your desired settings then conduct a blind ABX test.