I had a Sigma 18-200 DC (original design) and the 18-135wr at the same time, but my DA lens was not a great copy. The 18-200 was a bit better overall, especially above 100mm - but both needed some low-grade PP to sharpen them up. I'd give the bokeh not to the 18-135 though, quite nice! I later had a better copy of the 18-135 but soon after I was stricken with
DA-Limited Syndrome so the 18-135 was sent off. As to longevity I'd expect them both to be similar; the DC motor has a short history yet I have not heard of any failures - and DA*/SDM owners with bad AF demonstrate that people don't take such failures quietly!
The 18-135 has WR, which really needs to be evaluated for your needs too. If you're comparing HSM and DC I don't know which does the job 'best'.