Some general advice for you guys: Gunlines or even some shotting can kill a lot of stuff if its lucky. Heres my opinion on each unit, and a little advice on use for each.
The best mage in the game, whos automatically a level 4 mage, and has a 4+ward save. Yes please! What could be the bad part about this guy? Well, get used to it with lizardmen, especially characters:points. This guy is 325 raw, but you probably want him to have some upgrades. He can use any lore in the game, and can also choose 1 spell from one lore, and move on to another lore, Magic bests are these toads! He can also be upgraded in more generations, which gives him extra wounds, sometime an extra spell, and not suffer miscasts. I would upgrade him to atleast 4th generation, or 2nd. Nothing lower, or higher. Slanns may also take multiple plaques, which is useful. There are many magic items meant for him, which he should take. The diadem of power is one must have, and the others should be spent on plaques. He should probably have temple guard, which you may have 1 unit of per army. Temple guard must be deployed with the slann, and may never leave the slann. saurus warriors are a nice ccheaper option, if you want., You may also want to deploy him alone, but think about what a flyer unit or ambushers could do to it.
A very nice combat unit, and may even ride a dinosaur. Him riding a carnosaur is a magnificent sight, but easily shut down by dwarf thunderers or cannons. A cold one is a better option if you want him mounted, and all together he can have a 0+ armor save on a cold one, and a 1+ on a carnosaur. The battle option of lizardmen. Sadly, you really have to choose between the two in the lizardmen army. Ultimately, this guy can be very useful.
Pretty much a weaker oldblood, without being able to ride a carnosaur. This guy is really a must have in any list, unless its a magic heavy 2,000 point or higher list. Very useful, he can be a BSB(reccomended) but dont give him a magic standard, just a waste.
The veteran has a big possibility in builds, but the most common one is this:
Light Armor, Shield, Glyph Necklace(if an oldblood is in the army) or Aura of Quetzl, SPawning of Sotek SPawning of Quetzl,Charm of Jaguar, Great Weapon
What this build does is give this guy a 3 up save, 5 up ward or a 4+ wrd against S5 attacks, movement 9, stength 7, and an additional attack on the charge, so ultimately very good.
Light Armour, Shield, Piranha Blade, Blessed Spawning of Sotek and Quetzl, charm of jaguar
Light Armour, Shield, Maiming Shield, Blessed Spawning of Sotek and another spawning, preferably Quetzl, charm of jaguar
May ride a stegadon, but not reccomended. He can actually be very good, especially in combo with a slann. He has a very much supportive lore, and should only be used for mage defense in a combat list(oldblood led) and he should have the diadem of power if there is no slann in the army. A scroll caddy, kinda.
No comment. This guy is really bad, unless in a Southland list, or supporting a unit of skinks. If he has the scout special rule, he could be a nasty rear charger.
thats all for chracters! Best wishes, Kroq-Gar. If you have any comments or suggestions, feel free to pm me