Since we're able to keep valor, and many of the valor items are purchasable on day one, I'm surprised I don't see more talk about first day valor purchases.
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hit/mastery neck
hit/mastery bracers
int/haste-proc trinket
haste/crit finger
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are all achievable on the first day assuming its possible to farm at least to friendly on day 1 (please correct me if I'm wrong?). I'm unsure about honored, but I would assume not. I make a few assumptions based on intuitive logic rather than mathematical analysis, if those assumptions hold untrue than this information would fluctuate greatly.
I'm going to assume the crit finger is useless as the neck and bracers are itemized well enough to ignore it. For most, i understand the ilvl may make it worth something (alot of BiS farmers still use 489 rep or valor ring, or maybe 496 faction ring).
The bracers are essentially a direct ilvl upgrade from any HoF bracers (hit/haste/mastery interchangeably re-allocated to reach hit/haste caps and maximize mastery). But the 502 neckpieces with crit on them seem trumped by a long shot the 522 neckpiece without crit on it. And from an iLvl standpoint, the 522 neckpiece would trump any 489 neckpiece anyone might still have on just the same. Seems the neck is a no-brainer.
Trinket seems like a direct iLvl upgrade from EoT (except 10 seconds instead of 20 seconds), but I'm unsure of proc chances or ICDs. Assuming that balances out to make it a direct upgrade (please correct me if I am wrong), that makes it the equivalent to the bracers as a direct ilvl upgrade. I'm making the assumption here that everyone is upgrading EoT or RoY with 522 trinket, as LotC is almost untouchably good; please correct me if you know this assumption is wrong.
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So its based upon which of those slots is the least upgraded as of patch day.
If you're full 509/517 in every feasible slot; neck and ring are best upgrades.
If you're not wearing BiS as of now; it would be based upon what you're wearing now
currently wearing 509 wrists and 496 EoT or 476 RoY; then neck and trinket is best upgrade.
currently wearing 496 wrists and 496 EoT; ??? I would guess the wrists for simple matter that the cheaper valor cost allows quicker upgrading later on? I am completely unsure here.
And I'd assume no one has 496 wrists and 509 EoT, and if they did the assumption is very clear there.