Of the ones I've been able to do the math on, I get the best iMG return from Sky Plunge, followed in order by Starlit Night, Radial Heights, and Cloud Flight.
I didn't track Favor, and I haven't been able to keep records on Arbor Hollow yet.
At my level, cost to activate each card is 2000 iMG (not 5K as I reported elsewhere). The cards yield at least twice that in iMG profit. So, not a bad deal, but not something wildly better than a quick trip to the Ancestral Lands.
Anybody else care to chime in?