There no recogonized industry best.. If your looking for complete management you probably want to check out the CPA solutions... If you want more control and are only in a moderately competitive area a one-off solution could probably work..
Good place to start is Overture approved solutions (they have back end access to overture)
Why wouldn't you just focus on Google AdWords and Overture? From what we see, they account for 95-97% of the converting traffic out there; moreover, it's much easier to find a solution for those two than one that handles umpteen different PPCSE's.