McKesson Practice Partner is by far the best EMR out there. It is by far more robust and configurable than any other EMR. That is also it's weakness... it is configurable. Once configured to your work flow, actually helps you see patients faster and better. Tech support has been challenging in the past for McKesson but you can escalate your needs if necessary.
Another strength is it's end-user community and also PPRNET (Practice Partner Research Network). This network allows you to do community based research and also allow you to network with other users on quality measures. No other EMR has this!