I would have to say Blastoise. He is my favorite Pokémon and even though he is a water-type Pokémon he would still be able to dominate Pikachu because Pikachu has low hp points and one Earthquake move from Blastoise would be able to take out Pikachu with no worry. Pikachu is faster but his electric-type moves won't be able to knock out Blastoise in one move because his defence and special defence is very high. 
   Blastoise can shoot water from its cannons with enough force to punch holes in steel, and enough accuracy to hit an empty can 160 feet away. Blastoise also has the ability to learn Ice-type moves like Ice Beam and Blizzard. Since Blastoise is a fully evolved Water-type starter Pokémon, it can use Hyper Beam, Giga Impact and Hydro Cannon. It can spin very fast in its shell to knock enemies out of its path. Despite not having Steel as its secondary type, it does however gain access to Steel-type moves such as Gyro Ball, and Flash Cannon, which helps it in battles against types that resist its Water-type moves. If Pikachu and Blastoise were to ever fight, such as Gary's Blastoise and Ash's Pikachu, I believe that Blastoise would knock him out very quickly!

I'd say Manectric and Jolteon are better due to being electric types with faster speed and higher special attack. Also Raichu cause better everything trololol. Pikachu is only useful if it has the light ball, and even then it has to hold that specific item.

Ampharos is  better the Pikachu because Ampharos has the highest stats out of non legendary electric types.  And Pikachu sucks.  Even Magikarp is better than pikachu.  It gets to become Gyrados.

Dialga is way better than Pikachu becuase dialga can easily destroy him with one ancient power and ancient power is a weak attack.

lets see hm who should i choose. I hate pikachu very much.... lets go with Beedrill since his ability to learn moves that he is weak against is a great strength and Beedrill is even faster then Pikachu,

I say Vileplume, I love flowers. plus it's stronger.

  In my personal opinion I think that  Mew is better because first off  its a physic Pokémon and I am a big fan of physic types. Also  mew can learn any move that is not  exclusive to a particular Pokémon or Pokémon type. Mew is just so cute and  just a kick but Pokémon over all.

For me , I think that Dugtrio , Diglet , and other ground types are stronger than pikachu .. Also , allot of legendary pokemons are more powerful than that pikachu .. Pikachu is just one of the most over rated pokemon because he is Ash's best friend , partner , 1st ever pokemon , and the most over used , seen  , over leveled pokemon in all the anime series .. But for me , many pokemons can beat pikachu not only legendary pokemons even normal pokemon like  I have said earlier , dugtrio , diglet , graveler , sandshrew , sandslash , phanphy , donphan , many other ground type pokemons and other pokemons that has an advantage on thunder type battles ..
In short , ground type pokemons are better than pikachu , and not only ground types even other types .. They only need lots and lots of trainings to do ..

I think many pokemons are even more stronger than pikachu ! Pikachu is not the strongest pokemon in the pokemon world , many legendaries are 300 % stronger than pikachu !

klemish : a raichu on level 100 is a beas twith the moves that are fake blizzard pp99 accurary 100000 thunder pp99 accurary 100000 fire blast power 600 and pp 99 and acurary 100000 and its best move guillotine attack power 1 hit KO and accurary 999999