We have stayed at both. POR 2x and CSR 1x. If I had to choose a mod again, I would choose CSR. The reason? Buses, buses, and buses!
Both resorts are pretty.
FOOD: POR's food court, to me, was a little easier to deal with than the Pepper Market. Seriously, I am not a fan of either, though. I used to like POR's food court back in '97, but in 2004, their grilling staff needed lessons in customer service and I could say the same about certain areas of Pepper Market when we were there last month. PM has more options as far as food choices, I believe.
SIZE: CSR is definitly more spread out than POR, so that is a bummer. It is quite a hike from Casita's to the Dig site, so be prepared for that. I would not look forward to that aspect of it, but if it is not real hot or you are not really tired, it can be a pleasant walk. Other than that, it is looooooooong. POR, to me, was not as long of a walk.
ROOMS: Both are about the same, since they are mods. I like the CSR decor better. Cheerier, brighter. I do not like the pedestal sinks at POR. I like the sinks at CSR, more counter space. Plus CSR is newer, so I liked that too.
POOLS: CSR wins imo. Too bad their pool was like bath water, but that can be said for all Disney pools in the heat of August. It's just that the pool at CSR can accomodate more people and there are empty chairs to sit on, unlike many resort pools. I did like PORs quiet pool a bit better because it was easier to figure out the depths, but they were smaller than CSR's quiet pools, I believe.
TRANSPORTATION: This was the biggie. This is why I will not return to POR. I do not like waiting an hour two days in a row to get to MK during slow season. I do not like standing in a mile long line at MK to get back to POR, waiting for multiple buses before we can get on one, and then standing room only all the way back to the resort. When Disney recognizes that POR is a huge resort in desperate need of more buses to accomodate the masses, I may return, because I did enjoy everything else about it. CSR bus service was incredible. I was very happy with it. Minimal waits at the resort and minimal waits at the parks.

CSR IS a convention resort, though, so you might want to check to see if there are any huge conventions at CSR during your stay. This didn't bother us, nor did it affect us, but we left just before the start of a large convention, and I am not sure how this worked out for guests, because people were flooding into CSR to check in during our last days.
I think mods are a nice bargain and I would stay at any of them, but it will be CSR for us until changes are made at the other mods.

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