i like default better. the animations are the same, except the face itself looks more life like.
the custom character looks like their features have been sanded smooth. and when you select a rougher complexion, you get some 50 year old smoker's face. maybe there should be something in between smooth and pockmarked elderly.
The reason I wondered is before the game came out, I saw some screenshots of the default Shepard face and they looked WAY better than anything in ME 1 or 2. I'm wondering now if they were part of a cutscene video or something rather than in-game.