There’s no difference in terms of effectiveness — administer wherever you are comfortable. I also recommend rotating injection sites so your muscles have time to recover.

Also to consider
The larger the muscle, the lower the chance to miss (i.e., not hitting the muscle but a blood vessel). This can happen, for example, if you inject into the delt and it’s your first time or you haven’t done it recently.

There are studies showing that even subcutaneous is totally fine, will just get difficult if you’re using many ML’s in one injection then I would go with intramuscular injection.

I can advise you to use insuring syringes 29g to minimize scar tissue especially if you inject many times per week.
Some people avoid side Delts to avoid scar tissue which can be seen when you get really lean. I didn’t hav this problem until now but I am using small insulin syringes too.

Many people are still using way too big of needles.
I also like outer side of quads and chest is also very easy to inject.
Site won’t matter in the end because like I said it doesn’t even really matter if subcutaneous or intramuscular in the long run. When the ester reaches steady state levels in the blood after a few weeks you won’t feel any difference.

There is one argument for subcutaneous because it gets absorbed more slowly you don’t have such a High E2 peak like with intramuscular injection, so if you’re prone to high E2 maybe subq is a alternative for you.

This was just from me pinning in the arms for my cycle.

For best absorption you're going to want to boof it. But really though no it does not make any significant difference, IM is IM.