To make it short, I've had great experiences with Mellinger's. While my experience with them has been with placing large orders, I imagine the service level is the same for individuals.
My dealings with both managers/owners and the several staff i've met, have all been stellar! They all have bent over backwards for me and my friends and have been useful both with advice and any assistance we've need in keg selection and tap selection.
Their variety is the best I've not only seen but had to date here in Pittsburgh. I say this because previous to Mellinger's we had used another distributor who supposedly had a great selection, but could never deliver, nor even tried to deliver. Mellinger's only missed one of our selections once, and made up for it with apologies.
So to wrap that up: The service is amazing and the best i've had in Pittsburgh, and the selection matches as well.