which lens is sharper, Canon 24-70 or Tamron 17-50?

I am giving away my XSi to my brother. I debating whether or not to give him my Tamron 17-50 too and buy a Canon 24-70 for myself.

Depends on the body really. If I recall correctly they both scored similarly on the MTF charts....that is if you get a good copy of the 24-70 which can be hit an miss. (conjecture)

Just checked again. They are similar with the Tamron being sharper at the Edges.....the 24-70 has more range. the 17-50 is wider. I'd say you couldn't go wrong.

Personally, I'd keep the Tamron and put that money towards other purchases.

AF is much faster on the 24-70, though, but it is a massive lens. You'll also be starting at 24 which is significantly less wide than 17mm, even if it doesn't sound like it.

People tend to lean towards to what they have but the brick is a wise choice and you can always sell it and lose a little. I wasn't totally impress with its quality on a rebel body but when I mated it with the 5DMK2, I finally figured out why people love this lens. If I were you I'd ask people here with the 7D + the brick how they like it and how the image quality is.

I would keep the 17-50.
You'll start missing that wide range really really fast.

The difference between 17 and 24 is almost as significant as having a long 70-300 zoom.
Not in absolute numbers of course, but in "feel" ...