which network are you using?, in order to find your carrier firmware, we need to know the csc code, e.g. for me in the uk on three.co.uk the csc is H3G.....so i use either H3G firmwares or BTU (which is the sim free uk version, which is actually what my phone came with).
i think you can actually flash any, but you'll probably find best results (in terms of signal etc, as well as carrier specific apps preinstalled) if you flash your carrier specific latest firmware?
if you tell us which network you're on it will help with recommending a firmware?
on sammobile.com i can see 5 options for portugal:-
Portugal - MEO
Portugal (Optimus) OPT
Portugal (TMN) - TMN
Portugal (TPH) - TPH
Portugal (Vodafone) - TCL