I value Marriott points at 0.8 cents per point and AA points at 1.5 cents, although it’s easier to find significant “exceptions” to my valuation for flights than hotel stays. So the proposed trade wouldn’t make sense to me. That said, I might do it if I needed the AA points and didn’t have an immediate use for the Marriott points. I generally cash in about a million airline points and half a million hotel points a year, and I buy a lot of tickets for cash too, so I have opportunity to use miles or points only when I can hit my target redemption value. If you never travel to places with good Marriott redemption options then you may get better use of AAdvantage points.