I don't know about "best", but my
favorite recruitable commanders (this week
) are:
Tuatha, Vanadrotts, and Priest Kings (especially when the PK is your Prophet as well).
On the first two, Glamour comes in awfully handy, and their air magic complements this very well. The Tuatha can cast all sorts of valuable wide-area-of-effect Nature spells, summon up Firbolgs in the off-season, and has a javelin for stray infantry. As for the Vanadrotts, they are powerful (though expensive) sacred priest/mages, they get Blood (which is fun as Van) and they can also serve as summoning stations for all kinds of air-based goodies.
I never have my Tuatha nor Vanadrotts die due to projectiles in SP. Not to mention the fact that their Stealth values are incredibly handy.
Priest Kings can lead a townload of troops right from the get-go, and when prophetized can cast Fanaticism and Divine Blessing until the cows come home. Plus, mid-late game, they can be Improved Cross Breeders while they're waiting for something else to do.
[ March 18, 2004, 18:30: Message edited by: fahdiz ]