I have always been a sucker for Anthony Davis, but understand that Towns is making it a more difficult decision.
Roy makes a very good point with Lebron. It would be a situation much like when KG came to the Cs - we would certainly have some top flight years, but it would end too quickly.
I think it really depends on who your supporting cast is - are you starting from scratch (rookies, minimum level free agents, etc) or can you put a team like the Cs around that player? Davis, if the former; Lebron, if the latter.