Odds are enormously greater of humans on Mars planting our bugs there.

If I was in charge (and by gosh, I should be), the early phases of human Mars exploration would consist almost entirely of large manned orbital facilities around Mars. These would be operating fleets of real-time remote-operated vehicles of several types, giving Mars the checkout it really needs. The vehicles, of course, would be carefully sterilized.

Imagine what the Mars rovers could be doing right now if it was practical for someone to be running them with a joystick, and if a wrecked one could be replaced in a couple of days.

Oh, sure, do a few manned landings, just for the hell of it, but under strictly-controlled conditions with quick exits. No venting, dumping, bases or greenhouses for a while, until we're sure we aren't killing something native off.

It might take years to determine as best we can that Mars is really sterile, but they won't be useless years for science. And if it is sterile? Go for it! Start building bases and colonies if we want. Fill the place with Earth cooties, if they can hack it. Mother Nature would heartily approve--filling hostile environments with life is one of her favorite hobbies.