That's a tough call... I raced scrambles for a short time here in the northeast US. MX to me, scares me. I'm terribly afraid of heights and awkward in the air. I also speak on that as a experienced snowboarder - I dont do well in the air.
Anyway, Scrambles are quite fun, but you sure can get banged up in a hurry. You'll be forced to ride over, in, and through terrain you may not normally want to ride. That was my case anyway. In turn, those obstacles made me become a much better rider all around.
At 16, you're probably at a great age to do well out there. I was a mediocre C rider. I used to see some of the top 'juniors' lap me on my last laps. Those kids are crazy fast and usually dominate the top 10-15 overall results.
I loved blazing singletrack and the varied terrain. I hated mud pits. I did see a lot of injuries out there. Not sure how it compares to MX in that regard.