I switched from my 18MZ to the DS-24 this spring. I would never go back. Just FYI I just setup my Avanti XXL and I used 11 functions for basic stuff plus smoke and gyro. My BVM F-16 with uses 17. If you needed stuff like lights, canopy, speedbrake, AB LED, airspeed calls, etc you could easily run out of functions on the DS-16. IMO Danny is correct, go for the 24.
Gary

The main difference between the -16 and the -24 is that while both are 24 channel radios, the -16 can only have 16 assigned 'functions' (elevator, rudder, flaps, throttle, gear etc.) while the -24 can have 24 'functions'. On both, you can map multiple servos to a function, so you can fully utilize all 24 channels from the 16 functions.

The -24 has more processing capability to run more complex LAU scripts too.

On my Hunter, since switching to separate electronic air valves for the gear and doors, I have max'd out the 16 functions and had to dispense with my 'auto-brake on retract' function to stop the wheels spinning and rubbing the inner wing skin.

I've been flying with a DS-16 for at least 4 years and very happy with it. Tempted by a DS-24.

Paul