Which to choose for a beginner to start on R/C Submarine?

either, it's your choice. I just made an R/c sub from scratch, it's my second r/c sub. First one was a complete failure, but we won't talk about that now... Anyway this second sub that I have, I can go fast enough to dynamically dive, but if i wish, i can also lower the ballast tanks and make it sink. You can do just so much more with static diving submarines than you can with dynamic. I dove vertically 8 ft. to the bottom of my friend's pool and came straight back up, no throttle at all. Dynamically diving is easy, but having ballast tanks doesn't make it "harder" to control, you just need to remember to turn them off!

How do you keep the Transmitter from getting wet?

always wanted a 'flying' sub ever since i was a kid at modeling holidays where a guy had a dynamic sub bassed on a 2 liter coke bottle, looked like a fish and on full power jumped over 1m from the water. this was before the days of brushless, he had a very early type of mod motor.
my only problem is nowhere around here to use a sub, lots of water but none clear enough to fly one at that speed