Originally Posted by azraelck
This list is pretty much spot on; Rangers have a bit lower dps than Fighters or Barbarians, so you want the extra help against foes you'll find constantly at 20. In the raids list, a whopping 6 of them have an Evil Outsider of one sort or another. Elementals are scattered throughout the game, and also cannot be critted, you face constructs in four raids, as well as the portals in the Shroud, and pillars in VoN.
Giants and Undead can be optional though, as there are only two low-level raids (Reaver's Fate and Tempest's Spine) have Giant bosses, and the only high-level quest with any undead worth speaking of is Stealer of Souls (a lich) or Epic Wizard King (another lich), with the perpetually bugged, annoying to flag for, and no one actually runs anyway Abbot raid. Undead is invaluable while leveling however.
With a couple of packs and a raid featuring Abberations, that might make a good swap later; I believe Fireflash did so. She was short one being an Exploiter build (18/1/1 that could handle traps, dps roles, and was very survivable). However the list was largely identical: Evil Outsiders, Constructs, Elementals, and Abberrations. I don't know if two favored enemy bonuses stack, so I don't know if taking Lawful Outsiders would stack with Evil Outsiders (Devils are Lawful Evil), or Chaotic (Demons, like Mariliths, are Chaotic Evil). I doubt they do.