Well, lets see here, it depends on what size game you like to play, and whether you prefer to go with a combat lord or a magic lord choice.
If its a sub 2000 pt game, I tend to take the same thing regardless of what army i'm facing, a cold one riding scar vet and a couple of skink priests. Remember not to load down on magic items in small games, b/c a large amount of troops tends to do better than a singular tooled up hero, the more so the smaller points game you go. I've found skink priests on foot work best in pairs, and chances are with 2 lvl 2's you should get uranons thunderbolt (which does well against chaos warriors) or atleast forked lightning once. If not, no big deal, just use them to support your anvil of saurus with portent of far. This should really give your saurus the edge over chaos warriors. As well, a spear weilding saurus is three points less than a chaos warrior, before any sort of upgrade/mark. A huge mistake alot of choas players make is to load down thier core choice warriors with a shield and another type of weapon, making them crazy expensive for a single unit. Our saurus have close to the same stat line, only lower weapon skill, initiative and one less point of armor, and we should be able to outnumber them fairly easily. Try combo charges with saurus blocks and skrox/kroxigor or cold one cav. Since you should outnumber them pretty easily and all of your flankers are faster and harder than his, its alot simpler to gang up on his big slow block units of chaos warriors.
In 2000pts or better, where lord choices come into play, its your personal preference whether to go combatty or magicy. I've been running a slann/temple guard unit for some time now, only recently changing over to an oldblood on a carnasaur when I tried it for kicks and it worked awesomely. Anywho, with a combat lord, the oldblood/carnasaur can't go wrong, but to save on points, an old one on foot with the jag pendant (for those surprise leaps into expensive knight units) or on a cold one does pretty well too. For magic weapons, my first choice would be the blade of tzunki, followed by the enchanted shield, and the jag pendant if he's on foot. You'd be wounding on 2's with no armor save, and you should be getting the charge (considering chaos warrior blocks are pretty slow) so you should be able to wipe out his front rank easily. Even if you fluff your attacks, (its good to have a reroll or two saved from seconed sign) you'll have a good armor save, and good coldblooded leadership, so you can stick around in combat awhile. Even if you don't want to stay there, next turn you can just fly him out with the jag pendant.Just be sure to support your oldblood no matter his choice of mount with a few skink preists. The jag pendant is a low power bound spell, and doesn't work too well if its the only magic coming from your side.
As for magic, lore of metal is a must. Give your slann focused rumination, unfathomable presence (if your opponent likes the magic) and the plaque of tepok, then let him loose with the metal lore. Spirit of the Forge is what you're going for, it will annihilate huge units of chaos warriors. Distillation of silver isn't bad to support this, and transmutation of lead will give your saurus anvil/flankers another leg up in combat. Commandment of Brass is really the only "useless" spell as WoC tend not to have warmachines, but maybe a chariot or two could be set up for a flank charge.
Anywho, sorry so wordy, but hope this helps!
