Pokemon Black/White: Should I keep Ferroseed or Tynamo?

I only have one spot left in my party (Consisting of Serperior, The evolution of Palpitoad, Victini, (soon to be) That one pokemon you get from the plume fossil, and that one dragon pokemon you can get from the cave at route) and it's a decision between ferroseed and Tynamo. Which do you think I should choose?