Modem to choose topic

Hi, I have a i9300 galaxy. I'ts not network locked anywere, im from greece and using Cosmote as a provider.
Should i choose
I9300XXUGML2_I9300COSGML2_COS (this is cosmote fw)
or
I9300XXUGMK6_I9300OXXGML1_EUR (this is europe's fw)

Whats realy the diffrence between XXGML2 and XXGMK6?

Thanks for help!!