You will get plenty of opinions with this question! Probably will end up more confused than ever!
A couple general things....
You are asking about a "mid-range" zoom for your 7D. There are two schools of thought... Use one of the EF-S/crop mid-range zooms or use one of the FF design mid-range zooms. Some will tell you that "24-whatever" is a "terrible" range of focal lengths on a crop camera, but that's pure BS. What they are saying is that they prefer a different range... Not everyone feels the same way. Other folks use and like the 24-whatever or 28-whatever range just fine on crop cameras, thank you. You can built a fine system of lenses around either one! The other lenses in your kit, both longer and shorter, can be chosen to fit nicely with either a crop-design or a FF design mid-range zoom lens.
The other common point of contention is whether or not to go f2.8. Many folks want a fast lens for their mid-range, and with good reason. It would be better if you need large aperture for portraits and such, and you don't have some faster primes. However, if you are planning to get some fast primes such as the Canon 28/1.8, 50/1.4 and 85/1.8, you might not need to get a fast mid-range... It might make more sense to get a slower, but more compact "walk-around" lens, a better travel companion, and when you have the need for speed you can fall back on the primes in your kit. A slower lens typically covers a wider range of focal lengths, and in some cases is more resistant to issues such as flare and abberations.
So here are your possibilities:
The most compact, quality lens is probably the Canon EF-S 15-85 IS. It doesn't have big apertures, but it has a super range of focal lengths, in crop sensor terms... A bit wider than most. USM. Top image quality, though it's not an L (by definition, no EF-S lens ever will have a red stripe painted on it, no matter how good it is).
The fastest, quality option in a crop design lens is the Canon EF-S 17-55/2.8 IS. Narrower zoom range to get the fast aperture. Top image quality, mid-grade build. USM. There used to be some issues with dust getting in and IS failures, but we don't seem to hear much about these any more, so I suspect Canon has done some quiet fixes.
Now often offered as a moderately upgraded kit lens with the 60D and 7D, the EF-S 18-135 IS offers the widest range of focal lengths in a single lens. Image quality seems pretty good. A solid walk-around lens, but not particularly fast (f3.5-5.6), and it lacks USM. Still, this would be a convenient lens, covering a lot of useful focal lengths in a single zoom.
Then there are full frame capable options:
The EF 24-70/2.8L is the premium "fast" choice... the most expensive of the bunch. Well made, a workhorse of a lens, it works extremely well on 7D... Don't have any concerns about that. Anyone who says otherwise hasn't actually used it. I have... a lot. It is a big lens... nicknamed "the brick" for a reason... But is a very solid performer that a lot of pros use. It's quite close focusing and sharp throughout the zoom range. AF is USM, so quite quick and accurate. There are reports of variations... Well here's a revelation: Over time and with use lenses can get out of adjustment and need to be sent in for calibration. It happens with all lenses. Send it in for service and it will come back perfect nine out of ten times or better. Another revelation: When people spend this much for a lens they tend to be very critical and demanding of it... expecting perfection. No lens is perfect... This one is merely very, very good for a zoom.
The EF 24-205/4L IS is a more compact option, with a wider range of focal lengths, but of course it's an f4 lens. Also an L, it's quite well made and durable. Might be a more practical travel choice, especially for someone who is complementing it with faster prime lenses. T'aint cheap! But it also isn't as expensive as the 24-70. It does tend to have some rather heavy vignetting in the corners at the 24mm end, when used wide open. But this won't be seen much on a crop camera. It's a USM lens, too... and close focusing, but not as close as the 24-70.
The EF 28-135 IS... is sort of a "poor man's 24-105". It's not an L, but is much less expensive (downright cheap on the used market, so many have been sold in kits) and comes surprisingly close to the L's in terms of image quality. It is a variable aperture lens, and not particularly fast (f3.5-5.6)... but close focusing, has USM, and mid-grade build quality (roughly equal to the build of the 17-55 and 15-85, for example). It's close focusing, too... just not quite as close as the 24-105 or 24-70. Don't expect it to be as durable, long lasting or well sealed as the L's... But you can buy 3 or 4 or 5 of the 28-135s for the price of one of the L's. The weakest part of it's range is out at 135mm, where wide open (f5.6) it's a little soft. It has slightly more distortion than the two L's at the wide angle end, but doesn't vignette as much as the 24-105.
I've used three copies of the 28-135 over the years, all were good. I still have one as a backup/loaner/walk-around, to the 24-70 I primarily use. I don't have or need a 24-105. Nor do I want or need any of the EF-S lenses, mainly because I use both crop and FF cameras. But I also have always really liked the 24 or 28-whatever range on my crop cameras (that I used exclusively for 4 or 5 years). I find it a convenient and useful range, and simply match it up with appropriate longer and wider lenses.
One minor complaint... The 28-135 tends to have "zoom creep"... It tends to self-extend when carrying it around. The 24-105 sometimes does this, too, though less commonly than the 28-135. It's pretty easily fixed with a rubber band... But Canon could pay more attention to dampening the zoom mechanism on these lenses, or fit them with a zoom lock.
You really would have trouble telling apart images made with any of the above lenses, printed 11x14 or 16x20.
There are some other possibilities, but the above are currently offered Canon models. This doesn't even start to consider comparable third party lenses, some of which are pretty darned good, too.
There really isn't "better" or "best" among these... all are good. Each lens offers solid reasons someone might choose them and happily use them. I've never used the Tamron 28-75, so can't really compare (I know some Tamron have great image quality and are well made, I've used various of their lenses over the years.... Just not the 28-75). I suspect the main difference you will see is AF performance, particularly if you go with one of the USM lenses. Quite a few of the lenses mentioned also have IS, which is always nice to have, though personally on focal lengths such as these it wouldn't be a high priority consideration for me. (I do very much prefer to have IS on lenses 100mm and longer.)
Just pick the lens that best fits your needs and kit. I don't think you'll be disappointed.
