This is my first guide and I chose Falstad because of his mobility rather than damage, in competitive matches, a correct position is the key to achieve a good teamfight.

UPDATE: Seasoned MarksMan + Vampiric Assault is a very good choice to kill & sustain without consuming much mana.
At level 7 I chose Free Roll because it happens that you can miss your target with Hammerang nullifying its effect, and you must rely on a better chase\escape skill

Pros
+ With Barrel Roll you can fly over obstacles, no other hero can do that!
+ Excellent Mobility with Aerie Gusts for chasing down enemies and avoid damages.
+ Very good attack speed and range with Nexus Frenzy, it can be a devastating combo with his mobility.
+ Save precious Mana with Free Roll


Cons
- If you spam skills, you'll waste mana in no time
- Falstad is dependant on nearby team-mates