FYI, 'Lowest Guaranteed' != ''Guaranteed Lowest'.
The first would mean, imo, the price is the lowest price for a room at that hotel.
The latter is, as I understand it, that the room is guaranteed reserved for you at a price that's lowest then other places that will guarantee the room reserved.
Some places will book you a room but if you don't check in by a certain time, they hotel can cancel the reservation and re-book it. Guaranteeing it means if your plane gets delayed and you get there at 2am you'll still have a room. And if you don't ever get there, they'll still charge you for it.
Now, that's my understanding of how it works, but, I'm not in the hotel business just a semi-frequent business traveler. I may be wrong... or you may already have known all that. Figure some folks don't though.