Gear Advice.

[XmasMint]

I would say start with the class you plan to play the most, or the one you plan to take into Coil Turns 6-9. I don't know what your current gear is though for each class, do you have Relic +1 on each of these 3 classes?

If it comes down to equal play among all 3 classes, I would say start with the Healer of your choice.

While the weapon and shield for paladin are good, it won't make or break your situation with tanking and holding threat. You will gain a bit more Vitality though, so that's always a plus. However I feel for short term goals, these upgrades aren't needed as much. Something to aim for, but by no means something worth breaking your back over. (Again just my personal opinion)

However, with a healer our weapon damage is directly related to our healing amount, and the more we have the better. Not to mention the extra Mind added because of the higher Ilvl weapon will give us even more raw healing power. That being said, going from Ilvl 95 to Ilvl 100 won't see that much of a difference (assuming you have the Allagan Cane from turn 5). So I feel you could pick the best option in terms of upgrades on this one. For WHM that would be the Yagrush, and for the SCH that would be the Omnilex.

Which of course works out evenly because both require separate items entirely to obtain, so you could work on both at the same time so to speak. If you happen to finish your SCH Relic +2 first, then start on the Paladin one (or the WHM if the Yagrush seems like it will take longer to get).

Edit:
Keep in mind though, that Square has promised us further customization with the Relic +2 weapon, that will be released in a later patch. Which means you will be able to throw out the secondary stats of your relic for something far better, such as Crit + Det for your SCH, or Det + SS/Pie for your WHM. Getting it prepared now might not be such a bad idea.

I mostly alternate between WHM and SCH currently depending on what the party needs. PLD is just really for "farmed" content/DR only. I forgot to mention my gear =3. I currently have Relic +1 on my WHM(damn allagan cane dropped when I was on SCH). My SCH is using the Wave Codex from Levi, still waiting for Levi's mirror to drop. Both my SCH/PLD only have normal Relic. I can just farm for atmas on my WHM while getting the 900 myth to upgrade both my SCH/PLD Relics. Although currently, since the source of Unidentified Allagan Tomestone is still unknown...im leaning towards using the atmas for my WHM instead since I have the Wave Codex for my SCH already. So many choices >.>" Highly confusing..

I'm also currently debating what book to get next.

Omnilex Animus with
Spell Speed 40
Determination 20

doesn't look enticing at all, considering how much you have to do in order to get one. I know you will be able to customize it in the future but I'd be surprised if they just allow you to add another attribute, rather betting on "being able to add a couple more points on the existing attributes".

Tidal Wave Codex with
Piety 31
Determination 20
(Water Resistance 19)

doesn't look good either, the upgrade for it also drops from Levi EX so farming is required here but at least that's more fun than running after fates.

Weathered Book Of Diamonds with
Spell Speed 40
Piety 22

that's like the worst of the three. Does anyone know where you can get an "Unidentified Allagan Tomestone"?

But maybe I'm just too spoiled with my Twin book...

The weathered book of diamonds is horrible. I don't think I'll be getting that. 1300 soldiery(3 weeks) + 1 unknown source item and a random drop from coil to upgrade it is quite a waste IMO. As said earlier, I'm using the Levi Book while waiting for the mirror to drop to upgrade it. The increased magic damage on the i100 book should make it a better choice than the Twin book =X.