Okay, Oldblood on Carno is probably best Carnosaur variant right now because of his command ability, which gives any hero in 20" bonus 2 attacks on any weapon, including mount's ones. Since it is possible to stack same command abilities several times, Oldblood has highest damage potential out of 3 variants. He is very useful at missions, where only wizards and heroes with artifacts can score, since Seraphon wizards very squishy.
Ripperdactyls better than Terradons because they are more melee focused, while terradons have mediocre shooting and melee. With blot toad nearby, their number of attacks is really high. They also reroll all hit and wound rolls in seraphon combat phase. They are very popular as part of shadowstrike starhost, which allows them to drop turn 1 near enemy lines and instantly charge.
Skinks are not great fighters, so it is not really matter what weapons you give them. But boltspitters have higher range, and sometimes you want to kill that one model left on objective and some lucky rolls may do it. Starbucklers are better than clubs, because there are more difference between 6+ saves and simply removing models than may seem.
Solar Engine is nice artillery. It can be random and not too accurate, but long range, -1 rend and damage 2 are very good. Arc of Sotec is situative mortal wound weapon. It forces you to place bastiladon very close to several enemy units to be effective. Solar engine will really shine when you will have Saurus Astrolith Bearer, which gives it reroll to-hit.
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