The best pitches tend be from teams that gel and roles usually aren't essential for that to happen. I would say that whoever is a better presenter should probably lead, thats usually the CEO but not always. Whoever leads, the other person will do well to jump in when the time is right. Those spots can be when you need to hammer home a point and the other person sees an opportunity to restate something from a slightly different angle to make sure all the people in attendance are "getting it". Read the audience and both members of your team can drive the velocity.

When it comes to the technical parts of the pitch, certainly your cto will want to shine and show that he/she has the chops for whatever it is your doing. One thing I've come to look for though is a team that knows each other's roles a bit. The "non-technical" co-founder who doesn't know the difference between PHP and HTML come across weak in my book. The best founder teams really compliment each other but also have a slight bit of crossover. It helps you counter balance and spot check assumptions, etc.

Hope that helps. We could talk for hours on this as I've both pitched dozens of VC's as a founder trying to raise money, as an investor trying to raise a fund and an partner in an seed fund looking to back companies.