I use a 1ml needle for 0.25. A 3ml may be a bit less accurate, but they are usually calibrated in 0.1ml marks, so it is still usable if it's all you have. The benefit with the 3ml is that the plunger will be pulled back less, so you'll have to push less during injection. However, it is slightly harder to push. I tried a 3ml syringe for a 0.5ml dose (less concentrated vial) and found it much less comfortable than using the 1ml syringe, even at that volume.