8330:
CDMA
Sprint one will include Sprint TV, Music Store.. all those sprint extras
GPS .. NO WIFI
the 8330 is also supposed to come with OS 4.3 (if I'm not mistaken) which means video recording will be enabled amongst other things. I think with that OS higher capacity media cards work better too. Of course, you could install a beta of said OS on the 8320 if you wanted.
As far as which one you should get.. I would imagine it would depend greatly on your carrier. If you have Sprint or Verizon, you would need their respective 8330. If you have GSM.. you can get the 8320 and unlock it if needed. If the carrier is not an issue, take a look at the thread created a while back about choosing a carrier, I'm pretty sure it was part of the Blackberry 101 Lecture Series here on CB. It mentions factors to take into consideration for choosing a carrier. Remember that GSM carriers will have the new models first and if unlocked are convenient when traveling, as most countries use GSM and if your phone is unlocked, usually just need to pop in a different SIM.
In my opinion you should wait and get the 8330. It's a more advance Curve, 3G, and has GPS too; so the lack of Wi-Fi on it isn't a big deal. Plus even though the 8320 has wifi, surfing the web on it isn't any faster then EDGE.
