Reliability
Hygiene
The ability to breath through his ears
Can bench press 20 lbs with his tongue
I don't care if he can't tell me how deep the water is, but if he can stand beside the pool and tell me what temperature the water is......well, as Martha says, its a good thing.
But the number one factor that makes an ATF for me is when we can connect as friends and develop a more personal connection. It just makes all of the above 10 times better.
On a similar note, I have to say that the Happy Fuck Fairy (which, unlike Santa Clause, DOES exist), has truly blessed me the past few weeks. I don't know if it was the brief vacation I took, or just good fortune, but a few new names have been added to the ATF list. In the words of Damaaaan FUUUUUUUUCK YEAH!!!!! I love my job.