The Spotlights have been the best of the lot, that's not to say I haven't enjoyed the main series. After a shaky start with Infiltration it picked up but the strongest tales have been in the Spotlights, in particular the Kup and Nightbeat issues.
Spotlights take the lead for me as well. Some of the other mini-series have been pretty good, but overall the variety styles and tones of the Spotlights have made them more interesting on balance for me - we've had a horror story, a big ruck, a detective piece, a "movie action hero" kind of story... Each one has had a bit of freshness too it that has kept my interest level up.
I enjoy the Spotlight series the most probably because it reminds me very much of the Marvel TF series with its sense of a complete story in each issue but with continuing threads and a variety of artists and types of stories. Escalation comes second. Hearts of Steel had a stonking first issue but quickly faded. Infiltration reads better now than it did at the time.