Since I am bored I'm looking at the entire list of Grass types and will divide them into a few different groups. This isn't serious tier shit but it does come from a pro who has used far too many grass types when he really should have just benched them.
Boring Grass Types.
Victreebel. Enough said. Was originally the king of Growth.
Bellossom - Yeah it's kinda cute. It's got a bad movepool and you know who else is kinda cute and better? Vileplume!
Carnivine - If not for the anime he'd have to go in the catagory of so boring I forget it exists.
Simisage - It's actually useful like most of these other boring pokemon, but it gets less so as it goes along.
Adorable but not terribly good:
Jumpluff: He's useful, don't get me wrong (you can even surprise the fuck out of people using this in competitive battles) but its stats are LOW.
Cherrim: Is sooo cute, especially in the sun. You only ever see this on novelty double/triple battle teams though.
Maractus: Borderline between boring and adorable.
Middle of the Road:
Vileplume: It's cute, it's got some moves. It tends to die alot for whatever reason, it's in a lot of games.
Exeggutor: Is awesome, but not awesome enough. It can really shine in the right circumstances.
Meganium: Borderline adorable but not good, borderline boring if you don't find it cute. It's mainly brought down by being the second worst starter in his generation if you consider the makeup of the gym leaders.
Sceptile: Like Exeggutor, has seen better days when his best moves all ran off of special. Still really good.
Cacturne: Is fun but is now overshadowed by the other hoenn grass types including the other Grass/Dark!
Cradily: Almost belongs in its own tier of obscure pokemon that are impossible to kill. Sometimes I even forget just what grass/rock is weak to!
Lilligant: is the Beeheym of the gen V grass types.
Sawsbuck: Is fun and cool looking, and one of the few waiting for new moves to bust out of this grouping.
Cream of the Crop:
Venusaur: I love this fucker even when it wasn't good. Huge ass movepool, can do anything!
Celebi: Adorable, extremely rare in the US/EUR, we missed almost all of the events that released him. It's super Exeggutor.
THE REST OF THE HOENN GRASS TYPES: Ludicolo used to be the only good one, now the rest of them (Roserade, Shiftry, Breloom, and Tropius) all have their places on any in game team or most fun battle teams. What a difference the special/attack split and a bunch of new moves/an evolution did.
Torterra: Arguably the worst gen four starter (easily the worst competitively) is still a great pokemon with a cool design.
Abomasnow: Great design, great name, interesting type with the customary grass/anything huge pile of weaknesses.
Tangrowth: Defensive wall. Has some hilarious in game movesets and is decent in spots competitively.
Leafeon: Yes, it has no move pool. It's also king of Leaf Blade. I love this thing. You could make a case for boring, but I love it and it's my list.
Rotom Lawn Mower: Just look at that thing. C'mon son.
Shaymin: Either flavor is good. Regular one may suck in comparison but it has a case for cutest pokemon, let alone cutest grass type. Skymin is dorky looking.
Serperior: I like its odd combination of stats. Needs better moves though, B2/W2 helps, but not enough. Contrary will be fun.
Whimsicott: Prankster, that adorable fluffyness, who could say no? Kinda fun in game, shines in battles.
Amoonguss: This pun is too good. The only defensive spore user. Enough said.
Ferrothorn: Is Ferrothorn. Completely shamed the hell out of Foretress and stole Bronzong's lunch money.
Virizion: Shitty wireless but better than AT&T. FIOS owns. Also is special Breloom with worse movepool and abilities.
Bug/Grass Tier.
Leavanny: King/Queen/God Emperor/Empress of Bug/Grass Pokémon. It's actually usable despite the problems of this unholy paring.
Parasect: Is a zombie, it learns spore. I leveled one to level 80 something in Fire Red a few months back and things still went first and killed it. Still, it's a ZOMBIE MUSHROOM.
Wormadam: Count of hands: How many people in this thread forgot completely about this form? I thought so.
King of Shit Mountain:
Sunflora: Sunflora blows. Especially in Gen 2. I hate the thing. It's goofy stat distribution, It's weird first form, it's terrible movepool. Yes it can now technically kill everything with the right setup, but who can't? I do sort of like its design though.
So Awesome I Get to Mention it Twice:
Tropius: Alongside Mew, Golduck, Smeargle and a few others is an insanely useful HM Slave. Plus it has a cool Banana waddle thing and it's stats outside of speed really aren't that bad. I love this fucker.