2g only is very rare these days - only the cheapest of Chinese clones is 2G only. Most should be at least 3G. I'd not buy a phone that only did 2G unless I didn't want to use data at all.
As for what is best, it depends what's best for you. Do you need the higher speed data connection of 4G over 3G? What's the price difference (phone and tariff), and is it worth it to you? What's 4G coverage like where you are (if you don't have cover then it's no use to you)?