Cloyster

Cloyster is a top pick for a reason: it's one of the very few Pokemon blessed with Spikes, a very important move in a metagame filled with Pokemon that heavily benefit from the extra chip damage. It distinguishes itself from other Spikes setters thanks to its Water typing; coupled with excellent physical bulk and a powerful and relatively fast Explosion, this allows it to check Ground-types like Steelix and Marowak and act as a tricky-to-play-around offensive threat, since its decently powerful Surf keeps most Pokemon that resist Normal at bay that otherwise would be tempted to take the Explosion. Furthermore, Cloyster can further expand its utility thanks to its access to Rapid Spin, a very useful tool in a metagame where Spikes are so rampant, although it unfortunately cannot be used alongside Explosion.

However, while Cloyster remains the premier Spikes setter and Water-type in the tier, Forretress sports a typing with more resistances and an immunity to Toxic, which usually grants it more opportunities to set up Spikes than Cloyster. As a spinner, Starmie has a much easier time taking on Gengar thanks to its secondary typing and less trouble using Rapid Spin throughout the game by virtue of its access to Recover. Finally, due to its abysmal special bulk and subpar defensive typing, Cloyster is outclassed as a pure defensive Water-type by Suicune.