At the higher levels, the Marriott rewards are very hard to beat. My latest conversion was for 150,000 points (nominally 50,000 miles) for which I got 5 free on-season nights in Grand Cayman (worth a minimum of $2,000) and 35,000 miles deposited into my OnePass account. If you extend the second grade math, you can see that the real benefit derived from the 15,000 airline
miles foregone was over $133 per thousand (compared to the generally accepted nominal value of $20/thousand). Extending the math even further, you can see that the 150,000 points gave a total benefit of more than $2700 ($2,000+ for the hotel room and for argument's sake, 35,000 miles at $20 per to equal $700). This shows these points to be worth a minimum of $18 a thousand, or only fractionally less than airline miles.
I will agree with Bigtex 1 that Hilton and Hyatt have more better locations for awards, but I have no familiarity with their programs and doubt that their points can be as valuable as Marriott's (at the aforesaid higher level awards).
All this does not even value the points as highly as the 200,000 point award that IM4Travel described above, but I only have 5 days to spare in February and lots and lots of points for the summer.