Well it's a answer to a question of some time ago, but i just could not let this go bye, without my answer.
(Note the last part...my answer)
It is mentioned but to repeat...to compare these 2 is like comparring a flamethrower with a toothpick!
First: the toothpick
Terradons are Great. fast, effective and supporting your heavyweights, by eliminating threads fast!
Tactically challanging!
the score:
tactical +
speed ++
hitting power + (higher on a single character of course......)
staying power (cc) ++ (thank you hit and run)
To "hurt" an enemy with a toothpick is harder to pull off, but when you do

....man the satisfaction it gives!
second the flamethrower:
Everybody can hit something with a flamethrower. Everybody can burn things....Only a good general knows exacly when to burn and when to hit with it (yes! you can hit with a flamethrower...just not always the easy route)
Sallies are Super! Roasting everything within range! Packing a punch (s5, t4) and fear causing. The bane of everything low T, goblins, skinks, skellies, elves, human, the list goes on. No disadvantage on a missfire (losing skinks is nothing, compared to other miscasttables)
tactical: + (but a small one)
speed: ++ yes smoking the enemy turn 2 (or if your opponent began, maybe even turn 1)
hitting power: +++ No rolling to hit, just the number of hits!
Staying power: ++
My say..use 'm both!
but that's not a new statement also....
