We belong to the Cook Children's Physician's Network, and we really love both my girls' regular Ped and another doctor who we've used several times when he was the on-call physician after hours (and was actually my youngest's Dr. while still in hospital after her birth).
Dr. Mann is in Mansfield, so if you're South Arlington, he'd still be very convenient. Dr. Rain is right on the edge of the UTA campus, so it's a fairly central location to most of Arlington. They are both very kind, patient with moms who ask lots of questions, and love the kids - and the kids love them!
I am so sorry that you've had a poor experience... who the heck would staff an office dedicated to kids with a bunch of people who can't be patient with the situation?! Good luck - picking a pediatrician is big choice!