[Suicide Junkie]

Be sure to not just shoot straight at the tanks, that does very little damage, and you'll run out of energy really quick. Tanks hitting tanks, walls or being close to exploding tanks causes the best damage, preferably at high speed.

I suggest using your first points for more energy, and your second level for the type 2 missile and some stability. You won't need to get more missile types until you see multiple big tanks start to appear. Then grab the type 5 (yellow) one, which you can use to cripple one tank while you fight the other. In the meantime, buy toys and energy to use them with.