I contributed to that list. Even if the info is old, coverage can have only improved. If it seems out of date, that's because no one since then has bothered to email any updates. If you hike, don't follow the recent trend. Its the same with the Water Reports. Only a few hikers bother to email reports in.
The best coverage in the sticks is going to be Verizon as they have the largest network outside of the major cities. ATT is next best. This applies to any remote trail such as the CDT and not just the PCT. Most of the other carriers don't have any network outside of the cities or major highway corridors; so their coverage depends on any roaming agreements they have with other carriers which means you are less likely to find coverage. Sprint has great service in populated centers, but don't think you are going to be using it much in a deserted wilderness that often. I know many who had Sprint and T-Mobile that were borrowing other phones.
In SoCal Verizon and ATT are about the same. There are a few places where one or the other has better coverage but it averages out. But once you go north of the Sierras, that changes as Verizon is clearly better in many places. I had coverage with Verizon in some trail towns that no one did with any other carrier. Imagine what it would be like away from town.
There are 2 places where I remember ATT being clearly better then Verizon. One was at Lake Morena Campground near the border though you could find coverage if you walked 1/4 mile into town. The other was in the middle of the Sierra Nevada at Lake Edison where VVR is (even at the resort itself where the coverage seemed to stop, if you walked down to the beach, ATT would work).
Most of the time, I found that I could get a signal about once a day if I was actually trying. But there are some very remote sections where you could go several days without one such as the High Sierra and parts of Washington as there is no reason to put a cell tower in the vicinity.