The main thing to bear in mind is how the set is configured inside, and the interface available to you on the TX.
In this respect, the Robbe/Futaba and Graupner/JR sets take some beating, as they have the case designs and necessary junction points for adding expanded switch modules.
With microcontrollers it's entirely feasible to expand the amount of channels available to you well beyond anything you should ever need- how would 256 proportional channels grab you? Those channels would operate with a time lag e.g about 500msec, which isn't a problem for most auxiliary functions.
There are simple boards available, quite cheaply, that will split up one channel in to 5 switched functions e.g. - http://translate.google.co.uk/translate ... =&ie=UTF-8