someone gave me a bunch of 3mm pla, so I bought a ubis 3mm .4 diameter hotend, to replace my ubis 1.75 when I want to use the larger filiment... is there a difference in print quality if both hot ends have a .4mm diameter hole in the end???? Im confused!

Our Metbot 3D printer actually uses the same condition as yours, we can use 1.75mm or 3mm filament, and both use 0.4mm hotend.
Same model, same setting, some have different result. 3mm ABS printing seems not easy to have warp like 1.75mm, and the hotend seems not easy to get stuck like 1.75mm. I think the only good for 1.75mm is that it can use direct motor drive extruder, much easier extruder parts.