We currently use ADP and are based in MD. The customer service tends to be really spotty - we have in place a "3 call rule"- any ADP issue, question or concern, call the 800# 3 times, speak to 3 different people (that is not hard) and see if any of the answers match. I don't think there are that many solutions to the same issue. You never seem to get a staight answer.
We just recently made the decision to leave ADP for a Kelly Services due in part to a cost savings and a system integration. ADP has a lot of features, but it's hard to turn them on if you don't do so when you first set up.
It's horrible with accurals and even harder to change what you've set up. Every year we send the first two months completing manually updates, because our rollovers never work right. NIGHTMARE.
Best advice - compare, list pros and cons and make an educated decision. It might not be your decision, but at least you'll have looked at it from all angles.