Flyers are absolutely a double-edged sword. They are highly mobile and great at attacking, but you cannot protect a flyer with Guard, so they are very easily killed by mages with Reach, and flyers can't hinder non flyers which makes your opponent more mobile also.
About the "Fire vs. Earth" debate - if the elemental cloak did not exist, fire would clearly be the superior element for pumping out damage. However, elemental cloak not only exists but it is incredibly common in most decks. This really really limits the power of fire nukes compared to earth.
For any aggro deck it is important to have a sense of:
1) What timing do you want to hit? Round 3? Round 4? Or round 5? For a round 3-4 timing you should have a very good sense of exactly what creatures, enchants, and equipment you will have on the turn that you start rolling attack dice. Round 5 is difficult to fully predict.
2) For round 4-5 aggro decks, what is your plan against a round-3 aggro attack?
3) What is your backup plan, if your opponent sets up a superior defensive position (ie, an archer behind walls of piles with teleport traps and caltrops everywhere) Maybe you are committed to an early attack no matter what, maybe you use a "telefrag" to teleport the enemy archer out of his comfy nest, or maybe you fall back and build up equipment.
4) What is your backup plan against strong control effects, like a mind control or turn to stone? Do you dispel it immediately? Do you run away and let your opponent spend mana on Upkeep? Or do you press the attack anyways, overwhelming your opponent with swarms?