[Edit] Just checked with the friends. It seems like it really depends on the social habits. If a bunch of people started with gomen, then that word will stick, even if it feels weird.

For me, because I started with "arigatou" with them, so my friends naturally used "arigatou" around me instead. However, whether they use "arigatou" or "sumimasen" really depends on their family habits. Currently it's split 30(arigatou)-70(sumimasen) amongst them. Much nuance is learnt today.

So much of proper speech is dependent on who you are with and their preferred idom. Of course formality in the case of uncertainty is usually preferred, but that can lead to both humor and embarrassment.