I'm looking to upgrade my Canon kit lens which is the EF-S 18-55. When I zoom with it its now making a nice clinky noise Budget is around the 500 - 600 mark. I mainly use it to take photos of my dogs and cats and general use (portrait, landscape etc) I want something that's sharper and can handle low light. Of course with dogs they tend to move on you too!

Some of the ideas I've been tossing around are

Canon 50mm f1.4
Sigma 24-70mm f2.8

What I was worried about with the 50mm was losing the zoom (obviously) but I've seen some shots on this lens and they look fantastic, sharp and lovely dof.

With the Sigma - quality? speed? If I was loaded I'd look at the canon 24-70 f2.8 L lens but unfortunately its over budget

Would love to hear your opinions and suggestions