It would depend on what moves you teach them, their traits and evs. Personally I would say a dragon type or Sableye as Sableye has no weaknesses and dragons have very little weaknesses.
The most non legendary Pokemon is Charizard, Swampert, and Hariyama
Arceus
Mew
NO. Only ash got that as a choice. You have to catch it in the viridian forest, but it's rare
Pikachu
I know that there are 2 super rare ultra powerful Pokemon in the whole entire Pokemon world.Those Pokemon are Raquaza and Arceus, but what i know is that RAQUAZA is by far the most and i mean the most powerful ultra legendary in the entire Pokemon world.
The rare, non-legendary Pokemon in Generation I (Red, Blue, Yellow, Green) are:PikachuRaichuClefairyClefableVulpixNinetalesMeowthPersianFarfetch'dExeggcuteHitmonleeHitmonchanLickitungRhyhornRhydonChanseyTangelaKangaskhanStaryuMr. MimeScytherJynxElectabuzzMagmarPinsirTaurosLaprasDittoEeveeVaporeonJolteonFlareonPorygonOmanyteOmastarKabutoKabutopsAerodactylSnorlaxDratiniDragonairDragonite
Arceus
Caterpie
Arceus is the most powerful, with a base stat total of 720, the current highest. sds ooo
The most powerful water type is Suicune.
The strongest (most powerful) Pokemon is of course rayquaza.
Kyogre.
dragonite
Arceus
mewtwo
Mew
NO. Only ash got that as a choice. You have to catch it in the viridian forest, but it's rare