Cost and benefits in that order, but usually a combination of both.

I like FS Marriotts and also Westin, St Regis, and Luxury Collection properties. I will occasionally book a Sheraton, but it depends on the property as their are crap Sheratons and good ones. Hiltons have disappointed me for the most part and Hyatts are too few to warrant loyalty. IC brand is a combination of many lackluster properties mixed with those that are nice but few and far between.

I like RZ and 4S, but no loyalty programs. We are on FT after all, so I have to feed my point addiction.

So with FS Marriotts and Westin, St Regis, and Luxury Collection properties being my choices I pick from those. Marriott FS properties usually come out ahead on price, but keep in mind that I am one to plan 50 weeks out. I also do not book non-refundable advance purchase rates. SPG has a lot of these and if they work for you then great, but not me.

I recently stayed in Singapore. I checked Marriott, Sheraton, and St. Regis prices for the months leading up to my stay and none of them could beat the price I had booked for the Marriott. I book Marriott first and then when I do find a competitive price I compare things like location, hotel rating and qualilty, lounge availability and quality, complimentary breakfast if no lounge (not at SPG props or MR resorts), and other amenities (spa, fitness center, restaurants, etc). I weigh that along with the price and make my choice. FWIW, most (95%) of my travel is for pleasure and self paid.

Same goes for Hong Kong, Seoul (although I am staying at the Hyatt in December - reason: airport location), Bangkok, Sydney, Dubai, London. LAX upcoming in June I got a better rate at Westin than Marriott or Renaissance. JFK for next December I got a better rate at Sheraton over Courtyard. I actually would like to find some more SPG properties because I have already attained MR Plat for this year and would like to do the same for SPG to retain my Plat status. So I guess seeking status qualifying stays/nights is a factor also in determining where I stay.