It's easy to ditch starters in B2/W2 because there are so many better replacements.
Volcarona can be used to replace emboar. (Keep in mind it has bad moves at the beginning but great moves once it levels more).
Jellicent can replace Samurott (good moves such as shadow ball and surf and also great sp. defence. bad side is that frillish is crap. But has two great abilities like cursed body for any electric moves and water absorb for easy healing).
Ferrothorn or Lilligant to replace Serperior (Ferrothorn and rocky helmet for any physical attackers also doesn't have a bad moveset like power whip and iron head. Lilligant can have quiver dance and HP stealing moves like giga drain)
If I had the choice to choose a starter from previous gens, it would have to be squirtle. Not only is he my favourite pokemon, but Blastoise is bulky and can pack a punch.
All in all, you have to change up pokemon and find their strengths to really find what ones work for you.