I've used both and can honestly say that I have settled on Terumos. I had a lot of trouble with the BD syringes, specifically the needles "stripping out" when I tried to tighten them. Also, I felt the BD syringes seemed to "stick" (not smooth) while injecting. Since making the switch to Terumo, I can definately see a difference. For me, Terumo is the winner hands down.
As far as needle guage is concerned, I use 23G. I tried 25G, but it seemed too flimsy, and it was hard as hell to inject. My hand would hurt like hell by the time I was done. I use a 22G to draw from the vial, and 23G to inject. I find if you just push easy on the plunger with a 23G needle, the injection will be slow and painless, and no hand discomfort. I just think 25G is a bit too small for oil to pass through freely enough, IMHO.
That reminds me...time to stick myself!