We use to come to WDW so DH could run the marathon. (Now we live near WDW.)
For marathon we had stayed at:
CSR
ASMu
ASMo
Honestly, I would avoid the All Stars mostly because you will be sharing a resort with very young (and loud

) athletic goups -- and their loud buses. (Yes, we were at ASMu one year the same time as the imfamous cheerleaders, that were followed by even louder male soccer players.)
Disney does a good job of segregating like sport event participants. But I don't see that they do anything to control the negative behavior.
I would stay away from Riverside for the same reason. And probably FQ too just for good measure.
Depending on your budget a monorail or Epcot resort would be best.
If you are looking for a moderate, then I would stick with CBR or CSR.
When we stayed at CSR the resort did run out of hot water for us who did not rise at 3 - 4 a.m. to catch a bus to the start line. That was the only downside there. And whether that was just a fluke, hard to say.
HTH
