I think the answer is subjective, rather than objective, considering that you can't sell, trade, or barter Delta SkyMiles. Is there some reason you want to go to Europe multiple times, or would you prefer to see a bunch of different spots around the globe? Also, keep in mind that, with a RTW ticket, you can stop at two different places in Europe.
Personally, if I had the time, and the hotel points, to do it properly, I'd definitely do the RTW. Pity Delta's SkyTeam partners don't let us do it in First Class though