When Victreebel use only grass-type moves, Charizard is one of the best options. It uses fire- or flying type fast/charge moves which are very effective against Victreeble while cut damage of grass-type moves. It has high stats along fire-type Pokemon and its fire-type moves can get same type attack bonus (STAB).
Optimal moveset for Charizard to beet Victreebel is Wing Attack (or Ember) and Fire Blast. Usually Wing Attack and Fire Blast is considered as the best moveset for Charizard as an attacker. On the other hand, Ember is super effective against the grass-type Pokemon.
Other fire-type Pokemon works as well.
Pidgeot is easy to get. It uses flying-type moves with STAB are super effective against Victreebel and can reduce damage of grass-type moves.
Dragonite has high stats along all Pokemon, and grass-type moves are not effective against it.
For list of fire- and dragon-type Pokemon, tap the name of type below.
When Victreebel use only poison-type moves, Arcanine will be one of the best Pokemon to fight against it due to its attack performance. Arcanine has higher attack stats thant that of Carizard and can use Fire Fang which is more powerful than Ember. Arcanine cannot reduce damage of poison-type moves but use fire-type moves with STAB. Beating Victreebel faster means receiving less damage as a result.
Arcanine will be the best one even when Victreebel's movest is the combination of grass- and poison-type moves. Arcanine use fire-type moves are super effective against Victreebel with STAB while cut damage of grass-type moves. For the best moveset, refer notes above.