1) the IQ is a better session vape, FF2 is better for on demand. The FF2 is a terrible party vape (IMO), for example. If you have friends, and like smoking/vaping with them frequently, the FF2 is likely not the best device to buy.
2) The FF2 is better for concentrates in that it was designed for them and (though I don't use concentrates) all the reviews I've seen say that it works quite well with them. I can say from experience that the concentrate pads can be a bit snug and hard to remove, but again, your mileage may vary.
3) The app for the IQ definitely has more features than the FF2 app, the FF2 app is fine, but rather spartan. It is also certainly arguable that even after the firmware/app update the FF2 is more App reliant than the IQ (you can change FF2 temps to the 7 presets without the app now, but the fine tuning absolutely requires it).
4) Technique required. Near as I can tell the IQ has nearly zero technique required to use effectively.
5) Can't speak to the draw resistance on the IQ, but the FF2 is somewhat restricted. I don't mind it at all, but it is something to take into consideration if you do mind draw restriction.
6) Ease of cleaning. I don't know if the IQ is so much hard to clean as the FF2 is very easy to clean, as long as you respect the gasket.
7) The flavor the FF2 provides is amazing. That said the IQ is known to provide great flavor for a conduction vape.
8) Bowl size. One FF2 bowl is enough to get me all time, iirc the IQ has a bigger bowl but I hear it can be half-packed.
9) Water tool compatibility. IQ has 10mm compatibility out of the box with the long mouthpiece, the FF2 requires an adapter. I honestly never use the FF2 through water though (even though I have the adapter), the flavor is better without it.