Gogoat
- High HP and Attack
- Learns moves like Leaf Blade, Earthquake, Bulk Up and Horn Leech
- Sap Sipper is a decent Ability
- Can learn Surf and Strength
- Grass types often struggle in-game
- It's a bit slow
Roserade
- High Special Attack and Special Defense
- Learns moves like Giga Drain, Sludge Bomb, Shadow Ball, and Dazzling Gleam
- Budew is available slightly earlier than Skiddo
- Friendship evolutions are annoying
- Roserade doesn't learn anything by level up
- Less physically bulky than Gogoat
Both are good options, but I would go for Gogoat. It only comes one route later, is less reliant on TMs, and has more bulk (which is ideal for tanking super effective hits). You can use Roserade to great effect, but I've used both before, and Gogoat has generally been better. Here's a set:
Gogoat
Ability: Sap Sipper
- Leaf Blade / Horn Leech
- Earthquake / Bulldoze
- Brick Break / Bulk Up
- Strength / Return