The most efficient rabbit hole is the Beach Resort Tower. In 10x13 tiles you can host 42 visitors, so it's 3,09 tiles per visitor. Also, it cost 16,500€ to make the 42 beds, less than 393€ each bed.
The big one, Eco-Modern Resort Tower need 16x22 tiles to host 70 visitors, so more than 5 tiles each. Also it cost 542,85 each bed.
The colonial spanish one is a no brainer, more expensive (16,600€) than Beach Resort Tower, uses more tiles (10x29) and host less beds (40) so 7,25 tiles per visitor and 395,23$ each bed. Indeed, you can replace one of those for two Beach Resort Tower to more than double gains.