Sceptile, I like attacking Pokemon more but that's not my point. Sceptile has a better movepool and attack stats which is needed. Yes, Meganium has better defences but it's attack stats are poor and attack is needed in Pokemon battles. Also Sceptile is way better than Meganium in speed. Like Venusaur, Meganium can't learn Leaf Storm which would be useful for it. The one which is more useful is Sceptile again because it can learn rock type moves such as Rock Slide which nearly all it's weaknesses are weak to. Sceptile can also learn Earthquake which can beat poison types. Meganium can learn that to but can't learn any rock types and again It's attacks won't do so good if it has bad attack stats even with an attacking nature, it's attack stats will still be quite low. In a battle the winner would probably be Sceptile since it can learn flying type moves. In my opinion Sceptile has a better design too.