Hilton is bringing back “Fast Ways to Free Stays” for the fourth quarter. Between October 1 and December 31, every 4 stays or 10 nights earns a free night — or you can choose double base points after 4 stays or 10 nights. There’s no limit to the number of free nights you can earn, but free nights will need to be redeemed within 6 months from being earned.

Registration is required and you have to choose at registration which offer you want, you cannot change later.

There’s a long list of excluded rates which are mostly third party rates (like Orbitz, Expedia, Booking.com) though not exclusively so. And there’s a long list of excluded hotels which won’t earn credit in the promotion, from the Homewood Suites in Clovis, California to the Grand Hilton in Seoul.

The fact that this promo requires four stays for a free night limits the possibility of pure mattress running. Sure, an extra stay to push you over the top to the next free night can make some good sense (a cheap airport one-night stay to earn a free night in the Maldives or Bora Bora). But it’ll be a stretch to make sense at say (4) $80 stays, spending $320, to yield a free night. There’s a highly limited number of redemption options where such a calculation could make any sense.

On the other hand, perhaps bringing back free nights — something Starwood offered at resorts after 3 stays back in the Spring — makes it likelier that Hyatt Gold Passport could re-introduce their Faster Free Nights (free night every 2 stays) sometime during the traditionally slow winter months.

As far as how to choose free stays versus points, the free nights will generally be much more valuable but if you don’t expect to have good use for free nights in the first half of 2012 you’ll want to demur and take the points. Similarly, if you have especially long, expensive stays the points could work out. Or if you’ll wind up with 7 or 11 stays and an unwillingness to mattress run for the 8th or 12th stay in order to get the next free night then points could make sense. For short, cheap stays there’s no question that free nights is the better deal.

Sadly, for those of us unlikely to give Hilton 4 stays during the promo period, the offer does little other than a bump to base points which I don’t value nearly as much (which I suppose I can’t blame them for!). And I’m guessing this offer won’t move the needle on my own hotel choice between now and the end of the year such that I earn free nights. I have two upcoming award redemptions, and though award redemptions count as stays with HHonors towards elite qualification, they don’t count as stays for this promotion unfortunately.

Update: A typo in the post, now corrected, suggested that double points begin only after the fourth stay. Sorry for the confusion!