I say the last except I pronounce the sh a bit like a French J or the 'g' in "mirage". Just like "Cartesian". I've never heard the first. The second I've heard but I don't like as much.
That's what I was thinking, but I couldn't find a way to properly express the sound.
(Is Bayesianism even a word? Should it be? The suffix "ism" sets off warning lights for me.)
Visitors to LessWrong may come away with the impression that they need to be Bayesians to be rational, or to fit in here. But most people are a long way from the point where learning Bayesian thought patterns is the most time-effective thing they can do to improve their rationality. Most of the insights available on LessWrong don't require people to understand Bayes' Theorem (or timeless decision theory).
I'm not calling for any specific change. Just to keep this in mind when writing things in the Wiki, or constructing a rationality workbook.