They are both right next to each other,

Never stayed at the JW Marriott but from the public area I am surprised it has the "JW" brand and the decor is also a little "old world". Its also attached to a shopping mall.

Westin is newer and quite modern. Corner suites are very nice but with limitted view. Between the two, I would choose the Westin anytime (even if I have no SPG status).