Yanagi is purpose built to slice raw fish. It excels at that task, no other knife does it as well.
A yanagi slices other things well in some instances and absolutely piss poorly in other instances.
A sujihiki slices almost everything equally well.
Take for instance a big ass watermelon.....a yanagi is thick, and single beveled and would cut a watermelon like crap. A sujihiki would cut it very well. The single bevel grind on a yanagi would steer that sucker on a curve that would drive you nuts.
For what you want, a sujihiki works very well....and works very well at other things. A yanagi might work (I don't know exactly what you're cutting, how, etc.), but it would suck at cutting that onion you mentioned......and I mean suck.
I understand the bland look....very well.
I don't know that I would recommend one over the other. Kajihara has great steel, a good handle, and decent grinds (only ever seen the gyuto though). The Laser is a bit thinner, and I really like the steel.