I started my RC hobby with a Graupner MX16-iFS. I've been quite happy with it and don't have any plans to change in the future. As part of a package deal I purchased, I obtained a Spektrum DX7. While I won't be keeping the DX7, I don't have a receiver for the Heli I bought yet so I'm using the existing radio system in the mean time. Having thus had a chance to play around with them both, I thought I'd post a few of my observations.
- 8 channels instead of 7.
- Rotary knob. This can be used for flaps or throttle limit.
- More customizable buttons/switches. You can tie any function to whichever switch you like. The DX7 has fairly standard switch assignments and I found it hard to change the functionality. e.g., your elevator dual rate functionality can't be assigned to the aileron dual rate switch.
- Push button. Just another different style selector switch the DX7 doesn't have. The DX7 and MX16 have the same number of extra switches but it's nice to be able to use different types as suite your personal tastes. For instance, I find using the push button to switch my gyro functionality nicer than using a switch. Not that big of a deal really though.
- Easier to program. I found the menu system on the DX7 a little difficult to get used to. You have to push two buttons to activate the menu for instance. The MX16 feels a little more intuitive.
- Automatic timer. I tie my timer to my throttle channel or auto-rotate for helis. With the DX7, I couldn't find any way to start the timer besides pushing the button. (And it's hard for me not to forget to do that.)
Spektrum DX7 Pros:
- DSM2. You can bind-n-fly.
- Slightly more complex radio functions are available. You can add expo to your pitch and throttle curves for a heli for instance. Also has Revo mixing. (The MX16 has more free mixes though so you can do the same thing as revo with the MX16).
- More complex heli setup. MX16 only has two flight modes for helis. Normal and IDLE-UP. The DX7 has normal, idle-1 and idle-2.
- More model memory. The DX7 holds 20 models and the MX16 holds 12.
Anyway, I can't talk to much on the reliability of either system. They are both 2.4 Ghz systems and are not subject to interference from other transmitters. They both have to have an adequate power supply to the Rx which will reboot if voltage drops too low (not good).