^ I use 27s... it's all they've got at the exchange I go to (w/ 1 cc and 1/2 cc being my options). They work just fine. I DO have trouble hitting, being a female. I've had a few people help me out (and do most the time). Apparently I have 'great veins' but yet I still cannot seem to hit! For me, the reason I think I can't hit is the following: I get WAY too nervous (I can hardly stomach the idea of pushing a needle through my skin. And seemingly so deep - that needle looks freaking LONG). I have to really focus on my breathing and think about how relieving it'll feel to register and hit.

I was also originally holding the rig WAY wrong, like a pencil. I'm terrible with such objects (such as chopsticks, just can't do it) - I've now changed to hold the syringe properly. How do YOU hold it? Do you have a fairly steady hand?
Also, one clean jab is preferred rather than slow intermittent pokes, fishing around, etc. I think the key is to not over-think it (while practicing sterile technique).