I would say there isn't a significant difference (for most people) between Android 2.2 and 2.3. If you do prefer Android over iOS I wouldn't even worry too much about the apps that come with it since they are all basically equal once you start using the Marketplace. Just focus on the hardware you like best. I don't think its absolutely necessary to have "4G" or dual core but those two options are more future proof than 3G and single core.