Best size is the one that is most comfortable for you. I started out with 4mm for both basel and bolus but found that the basel dose stung quite a bit. At the suggestion of my DSN I tried 6mm which reduced the stinging sensation as the insulin does not aggravate the nerve endings near the surface of the skin so much. I now use 8mm for the basel and 6mm for the bolus. Ask you DSN for some different lengths you can try.
Interesting ref a longer needle not stinging so much. I rarely have any stinging with my Levemir and Novorapid with a 4mm needle. I gather Lantus does sting a bit more than Levemir but never used it
I have been in hospital and they used 8mm needles so it made me think that 4mm was small. But it seems 4mm is ok, thanks for all your replys it really helps.
4mm is adequate for the cast majority of patients (the layer of skin you have to pierce is less than 2.88mm in 95% of patients), so unless you are extremely obese (weight sorta requires at least height to judge) a longer needle will just force you pinch your skin or inject a an angle to avoid hitting muscle.