I'm thinking Stainmaster is a nylon................ is it?
Like Nick said. Best is nylon, but you're not gonna like the price difference. If it's a pet free rental, nylon can hold up really well and be cleaned. Cheap carpet as Nick said untwists and flattens out really fast. Next time you have to replace it, add in the price of removal and re-installation for a second time. If it's a nice place and you can keep good tenants, nylon might be a better choice in the long run. Buy a vacuum at the thrift store and give it to the renter so they have something to use.......... If it's supplied, they might actually take care of the carpet.
If the nylon is $30 per yard and the poly or PET is $15, the nylon might last over twice as long, being cheaper in the long run since you don't have to pay for removal, disposal and installation twice.