Suggestions on using Marriott hotel certs (+ United voucher)?

So the Chase Marriott Card is being discontinued for sad Canadians this year...we are getting certificates that expire within a year.

Any suggestions on best cities / places to use them? (Restricted to 1-5 category hotels.)

For myself, I am thinking of fall or winter as I already have a spring trip planned, no Marriott properties were appealing for the spring trip.

I also have a United Airlines voucher that I want to use. It was supposed to expire January but I got them to extend it another year with a processing fee.

I am thinking of:
a) Peru + Machu Picchu (Marriott in Lima) -- is fall a good time to go?
or
b) Las Vegas.

Last time I used a cert/points was in Tokyo (one of the Courtyard properties) and I'm not going back to Japan yet.