I'll vouch for the Tamron 28-75. I was considering getting a used Canon 24-70 F2.8L, but I decided to go with a new Tamron for a lot less.
I got mine after I had acquired a 70-200f4L. Having gotten a very high quality medium telephoto I found that I hated to go back to the kit lens because it just didn't compare. This was when I was at Disney World, I found myself trying to walk around the Magic Kingdom with the 70-200 mounted, and that of course didn't work out too well.
I'm a pixel peeper, I tested mine to see how soft it was when wide open (compared to the kit lens, famous for needing to be stopped down to about F8 for good sharpness). Mine is slightly soft wide open, but it doesn't have to be closed down much to get up to peak sharpness. My testing methods are crude and may be inaccurate, but that seems to be about the same performance as my 70-200 (which I'm thinking may be slightly soft, others claim it should be tack sharp wide open). It's still perfectly usable at 2.8.
I will say that I've noticed that my copy has a definite flare or internal reflection problem.. I'm not certain of the term, but a very bright light like a firework or illuminated sign at night can make sort of blurry mirror image on the opposite side of the frame. Not good, but.. it really does take a strong light in an otherwise dark scene, it hasn't shown up often.
I'll also mention that I've seen a lot of reports of bad copies of this lens. People sometimes report that their copy doesn't focus properly, or is too soft.. of course you can never be sure if you can rely on the reports people are posting, sometimes they report really weird stuff.. like a lens that is randomly soft in part of a scene, as if it defocuses unpredictably, sounds more to me like motion blur or something.. but it sure sounds like Tamron has some quality control issues. As such I bought mine from a local store that I knew I could return it to if I wasn't happy with it.
But I'm quite happy with it. It can't compare to the 70-200 for luxurious feel, it feels a bit cheap.. but it IS cheap, I really can't complain about that. The image quality is very good though.
Just be aware of the limits of a 28mm wide end. A lot of people feel that's limiting. I don't, normally, because I just don't shoot ultra wide very often. The only time it's been an issue for me was when shooting fireworks at the Magic Kingdom. But that's me, I REALLY don't shoot wide very often. I spend a lot of time zoomed all the way to 75, sometimes I use it instead of the 70-200 because of the drastically shorter minimum focusing distance.
However, there is a wider Tamron 2.8. They make a 17-50. But it's in their DI-II line, which means it's only for 1.6 FF cameras. So even though it's not EF-S, you couldn't use it on a full frame camera. I have no experience with it and can't comment on the quality, I think it came out after I got my 28-75.