There are a couple of "problems" with HGEC:
There are over a dozen variations (not including the original Exnem) so even though you use the EVE version and install the C cup you might install a mod and suddenly end up with a H cup when you try the (new) gear on. :blink:
I don't know if the other body mods have the same problem, but HGEC attracts a lot of modders who make showmanship pieces. Pretty to look at, but for me giving up three enchantment slots (body/legs/hands/feet all combined into one) isn't a good trade off.
(I won't even use robes due to the slot loss...)
1. 'I don't know if the other body mods have the same problem'.... Other body mods can have this problem, since in Oblivion(and Fallout 3), clothing/armor meshes replace corresponding body meshes literally. Though others do not have many variants as EyeCandy body does(Robert's Male body has some variants like slender, average, muscular, and some modder made variants of Robert's Female body).
2. Although the whole outfit is not so-good-trade-off for enchanting slot, if you're using OBSE and multi-enchantment mod, it doesn't matter so much(If you're not, it really does matter). Another thing is, some modders use his/her own customized mesh for clothes/armor making, and some may be incompatible with 'standard' mesh, making mixing-and-matching hard(namely issues about clipping and gaps between body parts).