I'd normally go for originals even if they cost 3x more than the 3rd-party equivalents (just look at my profile) but in this case, I'd say the 3rd-party options are really pretty close. So much so that the advantages of the L over the competition just isn't compelling enough. But that's based on the local pricing. $1800 is a pretty good price if you're comparing it to local prices. However, if you look at B&H, you'd realise that $1800 is only slightly under the price of a brand new set (without the shipping).
Anyway, I think you can't really go wrong with any of the 3 lenses since i think they are all great in their own right and will definitely do the job.