I've had both. The 8103 is a very capable radio - lots of usable functions, very easy to program, and uses an excellent case design (with the screen on TOP). 10 model memories built-in, "unlimited" if you pick up a Datasafe. The software supports functions specific to power planes, sailplanes and helis all in one box - if you fly multiple model types this is an Asset.
I sold my original 8103 when I upgraded to my 10sx2, then later upgraded to a 10X. At the time the 10X was the only model in JR's lineup that offered digital trims... I'd tried a mate's DT-equipped Futaba radio and was hooked.
The 10X certainly has more features than the 8103, and retains all of its user-friendliness regarding programming. The larger screen is a help here, as more information can be displayed at the same time.
One complaint - the screen is at the bottom of the radio, and the timer is displayed in the bottom-left corner of the screen. I find that I have to lift the radio up to chest height in order to check of how long I've been flying. With the 8103's top-center mounted screen a quick glance was all that was necessary.
I was flying power planes and sailplanes at the time, and for the most part the 10X suited me just fine. I noticed that the radio was quite a bit more power-hungry than its predecessors - many an hour-plus-long slope flight was terminated when the 'BATT LOW' alarm went off. I eventually swapped out the stock 1100 mAh nicad pack for a 1650, which solved that problem.
Then I started flying helis. Wups! Can't fly a heli with a 10X-Acro - at least not easily. I needed a heli-capable radio that was compatible with my existing PCM JR radio gear. With digital trims.
The 10X radios were still the only ones in JR's lineup that offered digital trims, as the 8103DT hadn't been announced yet...
I now have a matched set.
