I am considering a 70-200mm F2.8 on my D90 and use it mainly for portraiture.

Pros for Sigma:
-Full Metal Build
-Fast and silent focusing (thanks to HSM)

Cons:
-Tamron is much sharper
-1370g (too heavy for D90?)
-Costs $150 more

Pros for Tamron:
-Very sharp images
-Light weight (1112g)
-Looks better than Sigma's
-Closer focusing distance (although I already have a dedicated macro lens)

Cons:
-Plastic build (puts weight down though)
-Slow and noisy AF

The Tamron appears to be sharper than the Canon L series and Nikon's 70-200 VR, the VR II might be better however as a secondary student I am unable to afford one >.<

Body build is the least of my concerns (dropping either of them might not be a very good idea), therefore the question is...

AF or IQ?