My Cosmere reading order was quite weird: I started from Alloy of Law, then read through Warbreaker/Elantris, and then Mistborn Era 1. By then, Stormlight Archive had picked up pace, and I've been reading up everything from Way of Kings in publication order, as it all came out.

I've since done a reread of Warbreaker, as well as Mistborn Era 2 as the sequels came out. However, Mistborn Era 1 is a very crucial part of the Cosmere, especially as we get towards Stormlight Book 5 (coming this November). There's lots of spoiler-y reasons on why, but I can skip over that.

So, I'm re-reading Mistborn Era 1, hopefully followed by Rhythm of War (only Stormlight Book I've read only once).