Most people on FT seem to play the card game and thus have multiple cards that they use for various charges depending on the earnings potential. I use the following strategy:

SPG AMEX - All charges not put on the other cards listed below plus Starwood stays. Benefits of the card include cash & points options, premium award room options and airline transfers.

HH AMEX - All charges in bonus categories including grocery, drugstore, gas, cable, internet plus all Hilton stays. Biggest benefit of the card are the AXON awards.

Chase Sapphire - All restaurant and travel charges that don't go on chain/company specific cards. Biggest benefit to me is ability to transfer to Hyatt GP.

Chase PC Visa - Due to their recent devaluation (adding 50K awards) I only keep it for the annual free night and for PC stays.

I also have other cards (UA, BA, US and AA) but they don't get as much use as the SPG, HH and Sapphire cards.

One thing I am somewhat unsure of is if I should change to the Sapphire as my primary card from the SPG AMEX since I have a ton of SPG points and due to the creeping up of their award categories. Seems that some people have done this but I haven't.