I tried subcutaneous and I find some of the solution always leaks out vs IM where this rarely ever happens. Also, subcutaneously, a mass sometimes forms underneath the skin and is somewhat painful. I personally don't like this. In my own personal experience, I much prefer IM. Subcutaneously, it should absorb slower as there is less blood supply there.
I used to fear needles and faint just at the sight of them. Now, I do my injections myself and have absolutely no issues. It's all in your head, it can easily be overcome, you just need to be willing and persistent.