i don't think it's a matter of choosing which type of position to go for. most ib and im positions will be very similar and you will be completing similar tasks (dcf models, comps, meeting with clients...etc). during interviews, the questions asked will nearly be identical, especially on the technical aspect (a company has 3x ev/ebita, if its d/e is .7 and its cash flow is 10m, what's an approximate...etc). the behavior questions will also be similar. one big difference may be that during im interviews you'll be asked a lot more about what stocks you like and will need to pitch the pick.
especially in this economy, you'll need to apply to many finance positions and hope to land just one. some ib, some im, maybe some s&t, mc, vc...etc. while you'll need to focus most of your effort on finance, you should practice case studies and other areas just in case finance doesn't pan out. it's always good to have more options