I am using Exel's right now. I have used terumo's before. I think it is just what you like best, and price usually has something to do with it.
I use all 25ga. X 1" or 1.5" depending on the injection site. I have never used 27ga, but I guess if you get your oil nice and warm (I put my loaded syringe in a heating pad and stick it under my pillow while I am showering) it should work okay.
IMO if you are going to be pushing 3ml, get a 5ml barrel. It is easier to control when the plunger isn't drawn all the way out - especially if you are injecting yourself.