I've been playing an archivist bard archetype in a current campaign as a rationalist natural science-philosopher skeptic to great and awesome fun. He uses a combination of wands, social engineering, wealth, and his ever-present sharp wit to avoid being slaughtered by murderhobos and their ilk.
Mostly this is because it's a high fantasy semi-urban adventure, but it's also because if you roleplay a rationalist your single best weapon is his/your mind.
Also, carrying out experiments at the table, in character, is a ton of fun. Besides, it lets me break down all kinds of preconceptions and wander into trouble constantly. Also, this character makes a fantastic face for the party. Probably less so if your GM isn't cool with you using a combination of perception, diplomacy, and knowledges to manipulate people.
[[And HPMOR > OGHP, by a landslide victory. Quirrelmort == best villain]]