After about 4 years on Estradiol, my endo suggested injection. I had no problem with it for the first year or so, but then I found it more of a chore. I've always been queasy about needles, but one particular day as I was injecting, a little bit of blood bubbled up. Nothing horrific, just enough to say I want to go back on pills.
FYI, if you are going to inject, I suggest you hit a medical wholesale supply company. Where I live, the needle + the syringe part cost about $2.50 at the drugstore that did my prescription. Buying at the medical wholesale, I got a one year supply for $35.