Steel has half the thermal expansion of aluminum; my whole reason for a metal frame was stability, and with the steel it's nice to know I can move it around and it will not change alignment over time (even years). Also I had to have black, and the black powder coating was very good (none came off when tightening the screws). Also the steel is very very heavy; not sure of the aluminum weight, but I wanted the heaviest possible to avoid jumping around, and to avoid the printing being affected by vibrations in the room.

I now have the Lite6 dialed in, using black PETG only, and it works great. I would not use ABS:
http://3dprintboard.com/showthread.p...l-PET-filament