Flint and steel and wrath igniters might not be a good idea. It'll take a long time.
In 1.4.7 they changed how fire works so it burns out really fast and it can't spread as much as it used to. Thus, it's only good for traps or decoration.
Wrath igniters will burn up quickly because it's one use per tree. Not that they're hard to make, but spending diamond blocks to burn down trees isn't too efficient.
Turtles are a good choice, and you can also use TNT to blow the trees up.
You can also get a high potency enchant on the wand of digging from TC3 and just destroy everything.
You can also have the wand of equal trade with a high potency enchant transmute logs and leaves into ferns or tall grass. The ferns/tall grass will be destroyed instantly, and your inventory will be filled to the brim with saplings and logs.