I have stayed at both resorts multiple times and like both very much. If I had to choose, I would go with WL, no question. The bus transportation from MK at night, back to POR has been, in our experience, mosty awful. Long waits for the buses, crowds of people waiting for the buses, and you might not get a seat on the bus for the ride back, which is tough on parents with little kids. Getting to MK in the morning from POR was not good either, in our experience. Waited over 40 mins for a bus to MK to catch an early morning ADR. Ended up being late, despite getting to the bus stop early. POR is beautiful, the food court is great, but for families with little ones (my twin granddaughters are about the same age as your twins), I would not want to deal with POR buses. At least at WL, if you wait long for a bus, and you can't get a seat on the bus, it is a short ride back to WL, plus you have the option of taking the boat.
WL is amazing and everything is indoors. We love it!