You dont have to pick one if you dont see one that you like thats for sure.
That being said, you know best what your path is and what kind of people you would like to be around...in an online setting anyway.
So other than reading coven profiles, and looking at posters and leaders of groups that you like what they write....? The rest is up to you.
If you really want some kind of affilation, you can do Spellcasters, which is basically open to anyone and lets you post spells and stuff on the website.