I have no status with Marriott. I fly Southwest a lot, though, and working toward a companion pass; also, we like to rack up Hotels.com reward stays. I am wanting to use my CSP card to book two nights at a Springhill Suites in September and can't decide if I should book this room through Marriott ($171), Southwest ($179 and 750 points), or Hotels.com ($179 and 2 nights out of ten for a free stay).

Advice??

Not much need for Marriott status at SHS as they have have free breakfast and free basic internet. Are you planning to make more trips to be able to take advantage of the Hotels.com free stay? and does the virtual punchcard have an expiration date to finish and redeem that you can met?

Option 1 and 2 are almost equal value with option 1 being slightly better. I don't know where you are staying to figure the exact tax rate for the hotel but over two days you save $8 and $8 and figure approximately 15% tax rate on the $16 dollars is $2.40 for a total of $18.40. 750 points are not buyable at SWA but using the equal percentage and not counting the current bonus for buying 2000 or more miles you would pay $22.50 for 750 miles. By booking with Marriott you would get just a hair under 2000 MR points for you stay. With earning more MR points (10K total) you could redeemed for 2000 RR miles. So you would be 1/5 of the way to 2000 RR or 400 miles which would cost $6 to buy (If you could buy $6 worth of RR miles)

So option 1: Save $8, $8, $2.40, 6=$24.40
Option 2: extra 750 miles are worth $22.50
Option 3: would require 8 more nights and would depend on the cost of the nights and than the value of the free night redemption.

Since your goal is to get SWA Companion pass I would go with option 2 unless you plan to spend more nights at Marriott properties.

Not sure how the CSP card works to be able to do the math ie do you accrue more for hotel booking, versus airline spend etc

Chase Sapphire Preferred=2 points per $ for travel spend.