We stayed at POR earlier this month. They are both lovely resorts with great grounds. The themes are so well done. For my family, I would pick POR every time, for several reasons:
1.) The pool, slide, and hot-tub are very important to us. The slide at FQ LOOKS really cooler, however, it is much shorter and slower than the slide at Riverside. Also, the hot tub at FQ was a bit lukewarm AND is seperated from the rest of the pool. What this means is that when our daughter was swimming, if we'd been at FQ, we couldn't have sat in the hot tub and watched her from there or hop out to see if she had made it down the slide, etc. Given that these parts of the pool are imporant to us, this is a big POR advantage for me.
2.) Theming. I LOVED the Alliagator Bayou section, very our taste. Mansions are also gorgeous.
3.) Entertainment options: boats, carriage rides, fishing hole surrey bike rental, etc can be accessed at POR
4.) Food court at POR seemed to be larger and offer more options, service was also quicker
Who would I recommend FQ to?
-Anyone who loves the French Quarter and just really loves this theming
-Someone w/a very small kid who may be wanting to try a water slide for the first time
-Anyone who needs as compact a resort as possible for any mobility issues. The POR grounds are GORGEOUS, but, the resort is very spread out. We typically didn't mind the walk due to the pretty scenery. However, if you have reasons for not wanting to 5-10 walk to the food court, main pool, or bus stop, then FQ could be better.
Note, you can use the amenities of both by staying at one. It is not a far walk between the two, so, if you decide to stay at FQ for the compactness for example, you could spend 1 day at the pool at POR, or, go down there for a carriage ride, etc.
HTH!