Thank You for all your reply's
I am planning on using the 15-85 mostly for outdoors as this is where 90% of my shooting takes place. I do use the 50 1.8 exclusively for indoor, and was planning on upgrading that down the road with either the Canon 1.4 or Sigma 1.4.
What I was mostly concern with was image quality between the Canon 15-85 and the Sigma 17-50 for outdoor use.
I do not find it be much of a bother to shoot with a faster prime instead of a zoom for indoors. Just have to move the feet a little bit
as i often say, get them both side by side and test them out, I think lensrentals with take the rental cost of the final purchase? if you are in the us or canada that way you can play for a couple of days and get a feel for what suits you make sure you are happy with them but be aware a 2 stop aperture difference is very very big and gives you alot of flexability,