Las Vegas
If you're making a choice based solely on the room itself, but who really spends that much time in their room in Vegas?? (I guess it depends on which provider you choose to keep you company, lol)
Personally I love the red rooms at the Paris, this isn't the best pic but they are much more up to date than the awful classic rooms at Caesars. Also all of the red rooms have a strip view and you can see the Bellagio fountains pretty well from most of those rooms.
Now if you're looking for a swinging pool scene then perhaps you may want to stay at Caesars because the Paris pool is smaller and more tame but I prefer not having to walk 87 miles just to get from the casino to the rooms like you do at Caesars. Is it just me or do the constant additions/expansions make the Caesars Casinos feel like a bunch of classy trailers strung together? LOL
If you are a foodie then perhaps again Caesars may be a better choice Guy Savoy (pronounced Ghee Sav-wah) is one of those once in a lifetime dining experiences everyone should try!
Best of luck in your search!!
Here's a picture of the classic room... not so great!
I think the Paris Red Room is a wonderful place and the pool is nice and quiet and kind of low key, so I like that.
The other thing is Paris hardly ever has security at the elevators and it would be wonderful to have the view of the Bellagio Water Show while spending our intimate time in the Paris Red Room. 
Fun, and more fun!
XOXO
The Ceasar rooms are pretty run down unless it's in the new tower or the Penthouse suite. They also have a nice pool there as well. And ALL the red rooms have a certain atmosphere about them. That seductive, naughty feel. 