The 8-16 is fantastic, probably better than the 10-20 if you can live with the fact that it is a very wide lens (even 16mm is very wide) then go for it no questions. Just about bought it for my Pentax last year didn't because it felt a bit soft but the 10-20 which I ended up buying was not any sharper. I think it was simply the effect of the very very wide lens as opposed it being soft.
Having said that if you do not need to go that wide and maybe have a lens that is a fair bit more versatile sharper and really nicely made I'd buy a 12-24 Nikkor. S/h they go for 400-450 here which is cheaper than a new 8-16.