I personally really like the G27, and mine's used as well. The button placement is great, as you have 6 buttons on the wheel right at your thumbs so it makes things super easy like looking left and right, radio and changing info boxes on screen. The Porsche rims do look pretty comfy, tho, but is that worth that much more money to you? I also really like all the extra buttons you get on the G27 shifter. 8 extra buttons and a d-pad. Of course, it's only H-pattern and the Fanatec shifter comes with both H-pattern and sequential (I'd like to have a sequential stick).
EDIT: And oh, the G27's are pretty customizable, so if you really get into this, you could always put a different rim on it.