There must be a physical attraction and a feeling you are being entertained by a friend not a customer from the first meeting.
A compatible menu of sexual interest and a willingness to share something of her life as you share some of yours.  
And then there is that something extra - be it a look in her eyes, a laugh or shared prior experiences - that cannot be defined that makes you want to see the women again.

Is UTR, but I have only missed one month of seeing her since we met about a year ago.

She has become my ATF, for many reasons. First she is beautiful, and the type of beautiful that is at the top of my list. My people appreciate many different things, but her look is exactly what I love.
- Second, our time together is never routine or a struggle in any way, it feels very natural, how things flow.
 - Third, she makes me feel special, like I am more important than any other guy. She may have 10 guys that she treats that way, but I don't really care. It makes me feel special.
 - She shares things about her life as I share things about mine, and we both are anxious to learn more about each other.
- Last but not least, the sex between us is awesome.

due to my relative inexperience (I have only seen 9 providers other than her), but I cannot conceive of meeting anyone to displace her as my ATF.

She is
- very intelligent (her sexiest organ is her brain),
- beautiful,
- fit and encourages me to strive for improved fitness myself,
- a "people person" who made me feel comfortable with her the first time we met,
- the most considerate and polite person I know,
- strongly independent,
- a fellow foodie and awesome cook,
- a mentor and a passionate knowledge seeker, too,
- my most fun friend, who always improves any situation by being there,
- an excellent and timely communicator,
- an outstanding listener with a remarkable memory,
- not perfect (thank goodness, but she so mesmerizes me it took a while for me to realize it ).

She has been my partner in several adventures so far and hopefully many more to come.

I always leave her presence wanting more time with her and looking forward to our next meeting (which I would say is a good business model).

...the second two are more in the category of "necessary but not sufficient" conditions. The characteristics that keep my ATF my ATF are her intelligence and honesty. Yes, I find her beautiful and our BCD time very satisfying. But for me, an ATF is someone you see on a regular basis for more than just an hour date, and so compatibility, conversation, and mutual comfort are key.

Ladies: What about YOUR ATF?

Is there something special about him that makes you excited to see him?