While I do PREFER the cell shading, I think it all comes down to what strengths both offer. Cell shading offers a little more emphasis to what needs it, and can really make a piece "pop". While normally i think color's a double edged sword, looking at your works, you don't have to worry about something like that. However, BW and tones are arguably easier, and take less time to complete. All in all, I think it's up to you as an artist as to what directions you take yourself.