I'm not a ranger player ( I like wildshape too much), but I usually see people maxing out 1 FE, and spreading the other points around.
The theory is keep 1 maxed for the Instant Enemy spell (level 3, so available at 10th level) and use the others until then.
School enchantment; Level ranger 3
Casting Time 1 swift action
Components V, S
Range close (25 ft. + 5 ft./2 levels)
Target one creature that is not your favored enemy.
Duration 1 minute/level
Saving Throw none; Spell Resistance no
With this spell you designate the target as your favored enemy for the remainder of its duration. Select one of your favored enemy types. For the duration of the spell, you treat the target as if it were that type of favored enemy for all purposes.