The service is best in class with very responsive customer support! I have been working at this for almost 10 years now, so that's something to be appreciated as well :) They are always willing & able (and quite often prompt) when we need them most - during crunch time or otherwise.
We use their services primarily because of our close relationship w/the team there but they also offer some excellent value-adds like integration into Google Analytics etc., which has saved us many times over from having these additional tools built internally ourselves.