Primes vs zoom
I'd recommend you also consider the EF-S 15-85. More useful zoom range on a crop than either of the 24-xx zooms, excellent IQ, and 4-stops of IS. This was my general purpose zoom on my 7D before I went to a full frame, and if I still had a crop, I'd still be shooting the 15-85. IMO, for a crop,
I am concerned I wouldn't use it because of speed. But then I am buying a speedlite. I take your point though in comparison to the ef lenses. Does anyone know how fast the speedlights recharge vs the popup flash?
Don't really use my speedlight much, but I'm sure it's faster than the onboard flash. How much faster probably depends on which speedlight. You'll also get much better pictures with off-camera flash (onboard flash tends to give you very flat/uninteresting lighting).
it really comes down to the 17-55 vs the 15-85--the former if you want/need f/2.8, and the latter if you want the wider zoom range.
This I have heard many times. I think my question is I need to know how either compare to primes. Certainly much slower in the case of the 15-85, but in terms of image quality in general. I fear I will have the zoom sitting around not being used as with my kit lens, and keep my prime on the camera because it is faster and sharper and better all round.
The 15-85 and 17-55 will both give you excellent image quality. The image quality of good modern zooms really rivals that of most primes. Although a very good prime might still give you slightly better IQ, it's really quite close.
IMO, the primary reason to go with primes is their faster aperture. If you need that for lowlight shooting/subject isolation, then they're great. But of course you lose the versatility of a zoom.
BTW, you haven't told us the most important thing when it comes to lens selection: What you plan to shoot with it?
I like shooting shallow depth of field in natural light, portraits, city-scapes at night and I am interested in staged photography and narrative type shots. I also take candid shots of the kids a lot inside, but my kids are young and move fast indoors in low light with messy, busy backgrounds that I like to blur out. So in the house generally 50mm is fast enough in the available light at rapid fire to catch them and all the expressions, but often too close especially with 2 of them to get in the frame. 85mm would be fine on the odd occasion they're happy to indulge me for a portrait (but no good for candid), and outside. I heard the 85mm was a good portrait lens.
If you're really into shallow dof/natural light portraits, that argues for a prime. My grandkids are among my favorite subjects, and when I shoot them indoors, I use my fast primes--35 f/1.4L and Sigma 85 f/1.4.
I use > 100mm rarely and my 55-250 kit lens comes to the party ok in a lot of situations. I suppose I am outdoors with it so speed is generally not an issue, and it is light and I am happy enough.
I am concerned that 30mm on a crop won't be so good for portraits because of the perspective though. Until I decided it was just too much overkill to go for full frame, I considered a 50mm prime on full frame would be my walk around lens:-)
On a crop, I'd recommend you go with either a 35mm or 50mm prime. The new Sigma 35 f/1.4 is an outstanding lens and good value by most accounts, and would give you an equivalent (to full frame) focal length of around 55mm--a good all round focal length. Although 85mm is considered a good focal length for portraits on a full frame camera, it gives you an equivalent focal length of 136mm on a crop. Nevertheless, for tight shots, like head shots, an 85mm lens works quite well indoors on a crop, and also works well outdoors, where you have more room to back up. If you're interested in an 85mm prime, I'd recommend the EF 85 f/1.8. If you want a little better/faster 85, consider the Sigma 85 f/1.4 or EF 85 f.1.2L.