The Spa Tower room entrances are accessed in the hallway across fromr the conference center. It is that smaller tower that sits beside of The Cosmo. The only advantage I can think is if you wanted quicker access to Aria & Monte Carlo. I have never stayed in that tower, but would not have an issue with it.
I wish I could answer you on the slot selection, but it has been 15 months since I was in Vegas, and will be 5 more before I get back. But my favorite selections have always been Bellagio and Aria. Tend to do much better at Bellagio, but enjoy the slots at Aria too.
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