I asked the same question myself a few months ago and got Bitz 'N Glitz.... then ended up going back and buying Blacktrack, too. Both are lovely, and BnG is useable in most situations where you want black eyeliner, though it's definitely a soft black, and also makes a nice eyeshadow base for smokey eyes. The glitter isn't obvious but you can make the gold show up better if you apply it with dabs rather than strokes, or rub a brush head carefully back 'n forward a bit over it to give the "buff" effect. I also like setting b'n g by pressing beauty marked e/s on top, that gives a mix of pink and gold sparklies on a base of soft smoky black, I think it's pretty...
My problem with Bitz 'n Glitz - and it's a biggie, unfortuately - is that it really irritates my waterline, and I've heard from others (here, I think) that the glittery fluidlines are not advised for use inside the eye.... so it depends what you want it to do. If you're not someone who is bothered with liner under your eye, go for Bitz 'N Glitz. I love them both, but Blacktrack is the winner for me overall, because I do like that heavy black eyeliner look from time to time, and Blacktrack is DEFINITELY better inside your eye.