My current "standard" zoom on my 7D is a Tamron 28-75. I've had this lens for several years and it always performs well. IQ is amazing and the range suits me well. I shoot mainly living things (people and animals mostly), and have a Tokina 12-24 to cover the wider end of things.
If I have one small gripe about the Tamron, it's the slow focusing speed and the fact that it sometimes hunts or struggles for focus in low light, even in the studio (especially with dark-coloured subjects like black dogs). I like to do action shots in the studio (dogs catching tennis balls, etc.), and it's sometimes hard to grab focus with this lens.
I have an opportunity to buy a used Canon 17-55, but it would involve selling my much-loved Tamron to raise enough funds. I like the range of the 17-55 a bit less - I really enjoy the longer reach of the Tamron - but am hopeful that the quicker focusing would compensate. The new lens would be used for studio work, plus people and animal shots outdoors. I'd probably also sell the Tokina, and keep my 60 macro, 85 f1.8 and 70-200 f4 IS.
So would this be a good move? For those of you who know the Tamron and the Canon, which would you choose?