We have done both PC and Alaska, though Alaska was not on
DCL...the absolute deal breaker for us was that Disney didn't go into Glacier Bay which was the absolute highlight of the trip. Sailing in, several hours parked next to a calving glacier, and the absolute "end of the world" feeling in that bay can't compare with any scenery we've seen on earth. And we've seen some.
We did Alaska in late June, and it was warm, short sleeve shirt weather for the whole trip. It was certainly not a cold weather cruise. We did take one jacket, and wore it on deck at night (as we sometimes do in the Caribbean in the winter). And the trip along the inside passage is pretty cool.
PC was a relaxing cruise, with beautiful scenery (there are a lot cheaper lines than Disney for that so look at your options) with a lot of ports, and it should be on your bucket list, but since we've done both I feel good in choosing Alaska for your first one of those two options.
As for room choice, if you are trying to decide that, you'll really want a balcony for Alaska. Lots to time to spend outside early morning and evenings for the entire trip. Not as important at all for PC, since the sightseeing is all a single day of transit, and there are lots of great locations around the ship and on the decks to relax, read a book, watch the scenery go by and look for wildlife.