The first thing to note is that Dark Elves... are elves. What does this mean? It means that they are Toughness 3, and rely on their superiority in Weapon Skill, Ballistic Skill, etc. to defeat the foe. Dark Elves in particular are good users of magic, and can pack a punch in the Shooting phase if used correctly. The Lore you choose to use depends on the rest of your army, and how you plan to defeat them. For example, if you wanted to use your Saurus to beat them up in combat, then consider taking Life or Light, and using your Skinks to provide shooting support. The only real weakness of Saurus is their low WS and I in comparison to Dark Elves. I think you should take Life or Light. Fire is just magic artillery, which you won't need if you bring a couple of Salamanders to the table. Death, in my opinion, is perhaps a little short ranged. Your Skink priests will have Heavens anyway. However, regardless of the Lore you choose, you MUST take at least two units of salamanders. Why? Because elves so do not like a str. 3, -3 save flame landing on their troops - they're all t3! Also, ensure you have good magical defence... especially against spells such a Pit or Purple Sun.
As Hasnat mentioned you should pick a Lore that has a lot of synergy with your army, which generally means Light for combat lists and Life for the cookie cutter builds. Life is a very well rounded Lore that has good defensive spells, good augments and good damage spells. Dwellers does well against most elven infantry as most of them have S3, white lions being the only exception that comes to mind. The other popular Slann Lores are Death and Shadow. Death and Shadow are pretty bad since their damage spells are based on In tests, which elves passes easily and Mindrazor isn't very effective against poorly armored T3 troops anyway, especially compared to the Light buffs. The Hexes aren't fantastic against elves either, as they already have very low T.
From what erians said, I'd say take Lore of Life. I'd very much like to see those puny Dark Elves damage t6 saurus. Or perhaps take Loremaster for it too. However, do not be so quick to dismiss Light - ninja Saurus!
Being an Elf also means high point cost for each model. That makes magic missiles much more attractive, particularly Fireball as it can go to 3d6 hits. Wile I won’t say lore of fire is your best bet, it is more affective against elves than anything else. Even the Ruby Ring is a good buy.