The 28-135 was such a popular lens on 35mm film that Canon recreated it for APS-C as the 17-85 (not coincidentally 27-136 after crop factor is applied).
The 17-85 has an FL range that is better suited for APS-C, a newer and better 3-stop IS, and peforms very similarly optically to the 28-135, so between those two lenses, I'd go 17-85.
That said, you should be able to find the 17-85 used around $300, the 28-135 for even less.
If you're intent on spending $600, I'd keep an eye out for a used 15-85, if you're lucky you can find one around that price (or save a bit longer and buy it new).
I personally am weary of third-party lenses because of my fears of future body incompatibility and possible QC issues, but there are plenty on this forum and out in the world shooting Sigma and Tamron glass happily and without issue.