As Sceptile has a higher special attack than physical attack, I would go with Dragon Pulse (special, power 90, accuracy 100), Energy Ball (special, power 80, ac. 100. I know Leaf Storm is special, power 140, ac. 90, but it sharply decreases sp. attack, making it less reliable in a pinch due to accuracy and poor when used over and over. However, if you have a high-risk, high return play style, you probably would want to go for this).
As type variablity is importiant, I find it worthwile to stray some from your strong specail attack for the sake of strong physical moves including Earthquake (physical power 100, ac 100) X-scissor (physical power 80, ac 100).
What ever you choose, DON'T go for Solar Beam. If you used giga drain twice it would take the same amount of time, do the same amount of damage, gain you HP and not be as easy to protect agaist. Giga Drain is an OK alternitive for Energy Ball if you like to play it save as you gain HP and use a decent powered attack.