Just back from a stay at GF and have stayed at Poly twice. I've never, in those three trips, experienced issues with the monorail (and we used it extensively all trips).
Poly is a good location if there is an issue with the MK loop monorail (which seems to be the one with the most issues anecdotally). You can catch a boat to MK from Poly and can walk to the TCC for access to Epcot as well. When I stayed at Poly the first time, it was my dream resort too, so I'd say go for it!
Poly is a good location if there is an issue with the MK loop monorail (which seems to be the one with the most issues anecdotally). You can catch a boat to MK from Poly and can walk to the TCC for access to Epcot as well. When I stayed at Poly the first time, it was my dream resort too, so I'd say go for it!

That being said, I love the Poly and I suck it up and get on the monorail when I need to. I would never skip the Poly because of the monorail.
Besides, you can always grab an Uber if you are worried, probably less than $10.