I dont know about better....but it's better here in the US as it is an older, more established network. Today...more towers = better service. CDMA currently wins in that category here in the US.
GSM is relatively new over here. It's anyone's guess which standard will win out one day. Apples to Apples...I don't know which I'd choose.
CDMA phones do not use SIM cards. They are programmed directly by the operator. So you can't use any unlocked phone you wish. Only those supported by the service. And Verizon, the largest carrier, doesn't have many cool phones.
That has been my dilemma for some time now here is the US.
CDMA = better reception, crappy phones, less selection, no versatility in switching between phones at will.
GSM = so-so reception, better phones, unlimited selection & versatility.
Maybe that will all change one day.