Tastes differ (obviously), so I wouldn't try to impose my specific preferences on others...
My collection isn't that extensive, so my approach doesn't run to the big boxes (although I regret not jumping on the Bill Evans box in last summer's Concord blowout). So I'd look mostly to single discs rather than Mosaics or boxes. That said, I've long had an eye on the Farmer/Golson/Jazztet Mosaic, and to a lesser extent the Farlow (which is available as a Universal).
I'd first look at single CDs which have been on my wish list, or at Japanese imports of hard-to-find items. The ejazzlines.com inventory has really caught my attention, though a lot of the titles have trickled down to Amazon Marketplace at lower prices. I could easily go over $100 in individual CDs, which might leave room for a Mosaic.