Dan,
My current store is still with ADP, but my prior store (I still help out a bit) just changed to Dealertrack. I personally would advise doing whatever you can to stay with ADP, and trust me I do not like ADP all that much. If I was to look at another vendor I would at least give Quorum a look. The first thing I would do is talk to the Gilrie Institute at
www.paulgillrie.com, the cost savings they can provide when dealing with ADP can be amazing. Julius helped us out. Anyway I am afraid to be critical of Dealertrack since my current store is not on it, but I would be MORE than happy to put you in touch with the parts manager there, she would be glad to share her opinion.
Thanks,
Gerry