I am, right at this moment, very busy, so you guys should have plenty of time to discuss what the sets should be before I get a chance to write this up.
I feel like the main concern for venusaur is being able to do at least some damage to all the pokemon on the opponent's team. Venusaur is, as PK Gaming said, the best tank in the game, and it's extremely easy to switch in and get attacking. But if the opponent has a ferrothorn and you don't have HP Fire, for instance, Venusaur is just not contributing at all. It becomes far more of a sitting duck than the majority of outright walls, like chansey for instance. While Giga drain is nice against some things that are weak to it, it is often just a luxury, helping you more easily beat the stuff you do already. It doesn't hit anything like ferrothorn, heatran, or even scizor that can just switch in over and over again without even the slightest concern. I feel that moves like leech seed and roar do a good job of at least doing something to almost everything, while sludge bomb hits flying types, and EQ and HP Fire pick out the most frustrating opponents.
I would also like everyone to remember that there are occasions when it is acceptable to have many slashes on a set. It would be wrong to misrepresent what is and isn't viable. Venusaur clearly can't hit everything, and relies very heavily on the fact that the opponent doesn't know which moves it has. To nail down a standard moveset as the most effective is nigh-on impossible, because as soon as it became expected, it could be easily countered.
I also thought I would address PK Gaming's comments, since they don't relate directly to the moveset:
- I agree that the first sentence in the analysis should not be about sun, and that it's probably not even worth mentioning in the overview at all
- Venusaur's STABs are poor, and I'll stand by this. A defensive pokemon like venusaur would normally only run one of its STABs if it were actually good, and possibly no other attacking moves at all, but venusaur is forced to run both of them and at least one coverage move even to have a chance of hitting the entire opposing team decently. Grass is resisted by too much, and poison has one critical immunity that requires covering. To be honest, I could barely think of a worse pair of STABs to have.
-Venusaur's mega slot is significant. Yes, this is true of every mega, but I actually find venusaur to be surprisingly replaceable by non-mega pokemon, while this is not true of many others. I would sooner replace venusaur with an AV tangrowth or amoonguss than replace a mega lucario with an ordinary one.