I think the needle size that works best is the one that you will be most comfortable using. I've just started using the shorter needle and I think we've come up with a technique that will work for us. This morning I pulled the skin out on Buddha's side and shot upwards between my fingers (as opposed to sideways like before.) Not describing it well at all, I know, but I'm just saying that altering my technique will make them work for me. I bought 3 boxes (to save on shipping) and I intend to use them! Also, I'd been scruff shooting with 29 gauge 1/2" needles for over a year, and while Buddha never even seemed to notice that he was receiving an injection, his skin has thickened so now its hard to punch the needle in, and he's developed lumps too.