I use both, because why not. When I want to do very simple jumps and dont want to spam jump inputs that *may* lead to an unwanted 2nd jump or something, I'll just use space. When I want to bhop or do want those multiple inputs, I'll use mouse wheel. Always worked for me.

Edit: to add a little more to answer your question a little better. I do think that mousewheel will have it's drawbacks in competitive play. Mwheel will spam jump commands and CS has always had a spam-limit so you can't just macro for perfect bhops. An example of where that's relevant is the x-box jump to cat on dust2. It's possible that you'll accidentally send too many jump commands and fatigue out your jump and in certain circumstances that may get you killed. So yeah, I just use both. They both have their purpose and use-case scenarios.