First, I want to know your favorite typing, the Pokémon who represents it best, and why you like it...
My favorite typing is Water/Ground. This type is best shown through Swampert, who is the best starter I've raised, because of his wide selection of awesome moves and great stats. The Water/Ground typing has many advantages, such its only weakness to grass attacks, immunity to electric moves, and the ability to have great moves like Earthquake and Surf.
Now, for your least favorite.
My least favorite typing is the Ice/Grass typing. This particular typing is represented by Abomasnow or Snover, since they are the only Pokémon with this typing. This typing is abosolutely terrible, with six normal weaknesses, and one double weakness. Not only are there better Grass or Ice types, but they have better combinations out there. Ice/Water, for example.
So, you try!