why does t-mobile have the worst customer service out of the phone companies?

T-Mobile has been hands down the best and fastest customer service I've had and being an Android user, I've encountered some challenging reps but even they beat the likes of AT&T and Verizon.  The others in my household have AT&T and we have Vz for TV and Internet and nothing but real problems there. AT&T would say on the call they were going to do something and not do it.  Then I go into the store and they say the same thing and it still doesn't get done and their account is never updated with what they said they were going to do even though I asked specifically if they were noting the account. Vz jerked us out of or transferred our Visa card to other users multiple times.  The most difficult time I've had with T-Mobile is the reps lack of Android/Google knowledge.