[PhilD]

IIRC, the base RP of a Sage is 7, for a cost of 80 Gold.

The Daughter of Avalon has only 5 RP in a neutral dominion, for the same base cost, but since she's Sacred, she only costs half the upkeep.

It takes Drain 3 for two Daughters to have the same research potential as a single Sage, otherwise they are always higher. So, unless you're doing your research in a Drain 3 environment, Daughters of Avalon are always better in the long run (for research) than Sages. Plus, 2 Daughters will eventually get experienced and get a +1RP each, while the Sage will get a single point.

Of course, Daughters are capital-only, but in my book, anything that makes Sages uninteresting for research is a good buy (but that may be biased by the nations I usually play).

The Vaetti Hag of Jotunheim (55 Gold, not capital-only for 4 RP in a neutral environment) is also a good researcher; she will have a slightly better RP-to-cost ratio, since 7/80 is slightly less than 5/55, as soon as you're not in a Drain environment.

(I hope I don't have my numbers wrong...)

It would be nice to have a chart that lists, for each Nation/theme and each possible Magic/Drain scale, the best RP-to-cost mage available. Of course, you'd have to balance this against the upkeep-free undead (mostly, take initial costs into account)...