I would try either Aeros or Arix (when it's here) since you could use any old PC you have and have a NG experience since they'll be suing Linux drivers as their backbone. If you have an old Apple PC around then you can try out MorphOS as I beleive they have a try out period before registering. If you want to try out AmigaOS4.x then you can get a used Sam440 system for a good price nowadays since many users are upgrading to Sam460 & X1000 and good thing is if you choose to upgrade you will always find a buyer for your 440.
I don't recommend selling your classic gear yet until you feel satisfied with the NG experience. Personally I'm a hardware tinkerer guy and glad I kept my classic stuff now that i have more space in my man cave since it always costs you more to re-purchase stuff you sold in the past.