Kit Lense Replacement

[Geffen]

I'm looking to replace the 18-55mm Kit lenes on my 350D with something a little better. I'm mainly using it at the 18-24mm range at the moment as at the longer ranges i normally end up using my 50mm F1.8. The two replacements i'm looking at are

Tamron AF 17-50mm f/2.8 SP Di II XR
or
Canon EF 17-40mm f/4 USM L

What are peoples views on the two lenses. Tamron got price and faster lense going for it. Canon build quality excelent colour and i can use if on a full frame camera should i get round to buying the EOS 5 (Film) i want to get.

 

[Geffen]

Brought the 17-40L in the end. Like the idea of using it on a film body later, the snob value of having an L lense and build quality. Also i couldn't find any shops with the Tamron in to test.