You're at a Theme Park in the middle of Summer in Orlando. If you're trying to be around as few kids as possible, good luck.
That said, Portofino would have the least amount of kids- which will still be quite a few. It also has an adult only pool. Royal Pacific would likely be the 2nd least, but still, tons of kids there too.
It really doesn't matter though, since you're only there for one night- if you're trying to do both parks in a single day, theres no way you're going to have any pool time or resort time- so I'd just pick whichever of the 3 hotels that include express (Portofino, Royal pacific, Hard Rock) are the cheapest, tbh.