Twilight is the perfect VP. Great at organising stuff, incredibly knowledgable, and offering advice when things get tough.

But I'd always pair her with another Pony as President. Preferably Applejack, who has the right kind of mix of grit, determination and down to earth genuine-ness. I figure she has the right kind of mental strength to handle the childish and frustratingly confrontational world of international politics (at least, with a good team headed by Twilight Sparkle behind her to handle the fancy mathmatics).

Rarity would make for a very different type of leader, but I think she'd be my second choice. She can be a bit easily distracted perhaps, but she's very strongly principled and should be able to handle herself quite well on the diplomacy front, both in debates and international conferences.

(Also, let's keep the Real World analogies out of it. This is about brightly coloured Ponies running to be the first President of Equestria. Nothing else. )

Question is, how and why has Equestria moved to a presidential model? The returned Luna pushing for constitutional reform perhaps?