I have played with XMR and had a wallet on mymonero.
There was an option of a "3 mix" or something iirc. Does this equate to 3 ring sigs?
Yes, mymonero has a restricted range of mix factors for ease of use as the UI is intended largely for less-technical users. I expect as it matures it will have an "advanced" mode or some kind.
Using the native wallet you can use any factor you want, even >100.
(Lamentably exchanges inc Polo only do a 0 mix? which I assume means no-anonymity?)
I'm told Polo is using mix 3 now? I haven't confirmed that myself though. BTW mix=0 isn't "no-anonymity" though, as stealth-addresses are always used. I would call it weak anonymity for sure.