I just wanted to voice my opinioin that even though these are sister resorts under the large umbrella of Port Orleans, they are not "basically the same" or "very, very similar". They share buses, a marina, a sit down restaurant and a boat to DTD. Other than that, these two resorts are very, very different.
French Quarter has a Mardi Gras theme and Riverside has a Southern Country/Plantation theme.
Riverside has TONS more trees than FQ. This is one of the reason why I prefer riverside.
Riverside's food court is much larger (and better IMHO since it offers more).
Riverside's gift shop is much larger. I like it better than FQ but FQ does has some Mardi Gras items that are cute.
Riverside's arcade is larger.
The pool areas are themed very differently. FQ is much more colorful and festive.
The lounges are very different. Scat Club (at FQ) feels more like a bar in the city. River Roost (at Riverside) feels more like a lounge (and has a giant screen TV with sports on it). I prefer Scat Club because it has more of a city bar feel.
Riverside has the marina and the sit down restaurant.
I think the buses are a moot point. Everyone always mentions that FQ is picked up first and dropped off first. Yes, you are picked up first, but you then have to sit on the bus and drive through all of Riverside (sometimes only the first stop) before you head to the parks. i'm not complaining or saying this is bad, I'm just saying that I think the buses are moot (actually at any resort).
Riverside has 5 quiet pools, FQ has none.
Riverside has twice the amount of rooms as FQ.
You can easily walk from one to the other. It's 7 minutes from food court to food court. We did it many times last week. I love walking along the river.
You can see the high fireworks from Epcot from FQ (Top floor of Bldg 3 facing the parking lot for best view).
Personally, I prefer Riverside more. And the only reason why I prefer Riverside more is because of the feeling I get inside when I'm there. I can't explain it. It just feels like . . . . . heaven maybe. I don't want to say it feels like home, cause it feels like vacation. But it feels like I am 100 Million miles away from all my worries and stresses and it also feels like a million miles away from the parks yet still in the middle of diseyworld.
With that said, I also love French Quarter and would choose that second if Riverside were not available (although this situation is usually the reverse). French Quarter is quite popular and sells out fast.