Vileplume/Bellossom
Pros:
+Higher Defense
+Gets Chlorophyll
+Two different evos (I guess that's a good thing? I'm not sure)
Cons:
-Evolves via stone so its a pain to get
-More weaknesses
-Less HP / Special Defense
Tentacruel
Pros
+Higher Special Defense /Higher HP
+Can get Surf
+More resistances
+Gets Toxic Spikes
Cons
-I can't think of any
Overall, I'd go with Tentacool. Just watch out for physical attacks, its base Defense is pretty low.
Hope I helped!