Explanation:
The best Pokemon for me is one that doesn't feel like it is - Excadrill. It has the most versatility, most important utility and some key coverages. Besides that it can be used effectively in a multitude of different ways.
Mega Metagross can be used versitile and is able, thanks to its stats and moveset, to fullfill multiple roles. It can break defensive cores, provide Stealth Rocks and has some key coverages aswell.
Clefable is similar as the first two. It can do it all, from proving a wide variety of utility to function as a sweeper. Further has Magic Guard mon as a status absorber quite important, adding to the already good defensive coverage it provides.
Serperior and Weavile are on the lower end of the S tier for me. They both can check key threats aswell as function as sweepers or open up a defensive core.
Going down the tiers, the Pokemon either are less versitile, are less effective in the Meta or fullfill their roles less complete than the options above.
Mega Medicham for example has great breaking power, yet needs quite a bit of support to be effective and limits teambuilding capacities.
Gliscor, despite being a good mon, is usually just a secondary option for Ground-type and therefore less viable.
The B+ tier is notable, as it has a bunch of Pokemon that can be fantastic given a certain team or certain match up, but lack consistancy.
