Good point. I didn't realize it had been discontinued. I generally prefer used equipment for the economics. Though, after having to fix the 17-35 AF myself when it broke and canon would no longer support it, I've started to be a bit more leery about a lens that is several versions behind.
I've gone back and forth with myself over the 15 vs. the 8-15. I think the 8-15 is reasonably priced, but I don't know that I would use the wide end of it very much and question if the difference in cost could be better used somewhere else. Do you have experience with either lens? What types of situations would you want the circular image the 8mm produces on a FF body?
Over all I don't regret either lens, and am not in a big hurry to replace them even though the USM motor would be nice on the 35. Is either lens the best canon makes? No, but we have to be honest with ourselves as to what we actually need and what is the best use of our resources.
I've often considered the 35/1.4, and there is no denying the lens is sharper than either the 28 or 35's we've discussed, but it's also heavier, bulkier and more costly. The kit I described shooting with in school (28/1.8, 50/1.8, 85/1.8 ) could all be purchased together for less than the 35/1.4, probably less than the 35/2 IS if purchased used, and would give you a wider range of options while only being half a stop slower.
I apologize if it seems as though I’m lecturing. I just think we all struggle with wanting the absolute best (myself included), even though there may be a more reasonable option that will still meet our needs. Lately I’ve been trying to evaluate potential purchases as to what it will enable me to do that I can’t currently accomplish. If it simply does the same job better it usually takes a back seat to something that opens up other options.