If you ask RichRap he would say you need a geared extruder as he finds direct drive does not work well even for a 1.75 bowden extruder.
If you ask me I will say even less of a direct extruder as they have very limited resolution. What I mean is with each step of the extruder the volume they extrude is really high compared to a geared extruder. The numbers say the 2.7:1 gearing of Tantillus with 1.75mm filament is just about perfect if you want to print low layers and with 3mm filament the gearing limits how low you can go to about 80micron before you start having to make compromises.
So the answer is I would not go with another extruder unless it is geared and possibly a higher ratio then 2.7:1. But as always you can use whatever you want even a direct drive like the Airtripper one.
