well there you go....at least now i understand why you are trying hard to get the sprint sim card to work on your phone. why don't you just put your phone in roaming under using gsm? i bet that'll work. what plan do you have with sprint that comes with international roaming and international data free?
and as far as your question about which is better...it really depends on the person which network/carrier is best for them.
edit:
you can probably set your phone to gsm and then try this cab
http://forum.ppcgeeks.com/showthread.php?t=105779 to turn on your roaming.