I have the Doxy 3 and have used the original Doxy. All Doxy’s should have the same power, so from that point of view it shouldn’t matter which one you buy.
Generally I prefer smaller surface areas to my toys (so bullets over pebbles for example). Wands tend to be ok for me due to the sheer power involved though. I do really like my Lovehoney Classic Wand but it rarely gets used now as I prefer the Doxy 3. I find that the Doxy 3 has more power, more directly delivery of that power and a slightly higher frequency of vibration (not enough by a huge amount though). All of which really work for me.
I’m really looking forward to seeing some reviews of the new Doxy 3R. If it is anywhere near as powerful as the 3 (which the marketing says it is), I’m definitely getting one. Not many reviews about yet and not seen a comparison one