Foreflight works with both Stratus and Garmin transponders. Stratus connects via wi fi, and Garmins hook up via blue tooth.
I prefer the Stratus wifi hook up, as then I can tie the I Pad Foreflight into the blue tooth in the headset and get audio traffic, approaching runway, caution traffic alert, etc.
Of course you could always hook into a Sentry or something like that as well, but I can't see spending that when the transponder connection works so well giving you traffic as well as WAAS GPS accuracy.
(VFR flying only - no IFR of course)