I am guessing your brewing a 10 gallon batch?
I brew mostly lagers and I love S-23. I was better able to understand it's flavor profile when I started using it in my BMC clone, it can be a bit fruity and have a strange sort of sweetness when it hasn't been left to lager for a few weeks, but nothing crazy. I really never detect any sulfur from it in the finished product either. I've used it at ale temperatures loads of times as well.
I've saved it for up to 6 generations before too and didn't notice any wild changes.
Comparing it to 34/70 is hard for me because I never needed 34/70 really because I was always so attached to S-23, but maybe....maybe 34/70 is a bit cleaner. I just brewed a pumpkin lager with 34/70 though, was fantastic! I do not know about the attenuation of 34/70 vs. S-23 but I've had no problems getting S-23 down to lower than 1.004 or so for my American lite lager clone. Actually, I'm going to try 34/70 on my next batch of it just to try and learn it's flavor a bit better.
Either one you choose you can't go wrong. When dry yeast is available for the particular style of beer I want to brew, I use it. No starter, no risk of contamination or worrying about how healthy the yeast are either. I don't know if I've ever used 833 or not, so I can't help you to compare. Personally, I would choose the 34/70 though, and leave the S-23 for when you want a nice fruity German Pils or an IPL. I think I used 920 on my last batch of Bock and I don't even remember why I chose it now.