i would check out some photo forums/review sites and find out what everyone is using.

couple of good ones:

http://www.fredmiranda.com/reviews/

http://www.dpreview.com

http://www.canonlensreview.com/

i had the tamron 28-75 f2.8 and LOVED it, it rarely left my camera but the macro on it wasnt the greatest in the world

sorry i couldnt help more