Who in the world dives whitewater? I've dived WV rivers for 45 years and I've never experienced any sort of "tumbling." Yoke type regs are all I've ever used.
Kayak (not raft) the New or the Cheat or the Gauley if you want some
real fun.
Most of the major brand name regulators are fine. Yoke is the most common recreational fitting in the USA. DIN is more secure, but if you rent tanks then you're going to need an adapter so that your DIN regs will fit on a yoke tank. Might as well stay with a yoke fitting.
When I take my DIN tanks to be filled most places don't have an adapter, so I have to supply my own (we're talking Appalachia here).
What to look for in a regulator:
1. Service - can your regulator be serviced locally, or will you need to send it to Florida for annual maintenance? Check with your local shop to see what regs they can - and can't - service.
2. Ports - How many ports does the first stage have? At the minimum, you need 1 high-pressure (HP) port for the pressure gauge, 1 low pressure (LP) port for the primary reg, 1 LP port for the octo, and 1 LP port for the BC inflator. That's 1 HP and 3 LP ports. If you have a dry suit, you'll need another LP port for the dry suit inflator. If you have or want other fancy (unnecessary) gadgets, then you may need even more HP or LP ports. But most people will do well with either 1-HP/3-LP or 1-HP/4-LP ports.
3. Piston or Diaphragm? The innards of a piston regulator first stage are exposed to the water. If your water is clean, then it doesn't really matter. But if the water is dirty, then it's best to stay with a sealed diaphragm.
4. If you like the Oceanic, then get it. You'll have your regulator forever, so get what you like or you'll be spending double to replace it with something that you do like.