We stayed at CR last year, haven't stayed at the Poly (yet!) but have spent a lot of time at the resort.
IMO, both are fantastic transportation-wise. The walkway from the CR to the MK is absolutely wonderful! Getting in and out of the MK can be a nightmare, especially at closing, but the walkway lets you bypass all of that chaos.
That said, points to the Poly for being able to walk to the TTC. If you're going to Epcot from the CR, you will have to change monorails at the TTC. Not a massive inconvenience, but an inconvenience none the less. From the Poly, you would just walk over to the TTC and get right on the Epcot monorail.
I really don't think you can go wrong either way!