i'd start with a bent shaft. They feel totally different and once you get used to one then it is hard to switch.
I had occasional wrist pain with my straight shaft. It was a rough few weeks to get used to rolling with my bent shaft but I never had wrist pain again.
With a straight shaft I think it is easier to lose your key when you are upside down and your paddle and head are bouncing off stuff. Losing you key is what happens when you loosen the grip on your key hand (probably right hand) and the paddle spins a little bit and you have no idea what the blade angle is and you have to reset your key by feeling the blade with your hand while you continue down the creek with your head bouncing on the bottom and sieves approaching.
A bent shaft naturally fits in your hand in the keyed position so there is not so much guessing about if you have the key right when you temporarily lose your grip and then grip it again.
Not only does a bent shaft take it easier on your joints, I think it is easier to generate power with one. It makes sense to me.
Think of it this way:
straight shaft = bent wrists
bent shaft = straight wrists
If you punch someone in the jaw with your wrist bent who knows what is going to happen, probably a hurt wrist and a counter punch to your jaw (straight shaft).
If you punch someone in the jaw with a nice straight wrist the lights are going out (bent shaft)