Without question, I would choose the 2 Person AMK Heatsheet over the poncho. The Heatsheet is nothing like the traditional space/emergency/survival/crap blankets -- they pack smaller, are reusable, are considerably more durable, and don't make a fraction of the noise that the aluminumized mylar blankets do.

Please don't take this as an insult, but based on your choice of the mylar emergency blanket shown in your kit, I'm assuming that by "poncho" you are actually referring to one of the $2.00 disposable ones, correct? I rate those just about as useful as the mylar blankets...

If you are actually referring to a nylon tarp/poncho (which is considerably larger) then it would be a somewhat tougher decision.

The Heatsheet will not only keep you warm (unlike a disposable poncho) but may also be used to keep you dry (especially if you were to hold up stationary and wait out the rain, if possible) and will provide a very reasonable improvised shelter.

Jim