I wish there was a way to see the results without answering...because I can think of a few other options (which may only exist in my mind, but they'd still be preferential to me!).
I'm at the point where I hate the magnetic key cards. Over the past couple years, we've seen them "failing" more and more often. "No problem," the front desk will happily key more cards. Only this always happens, of course, to ONE of us (me or DH), and unless you re-key both at the same time, it locks out the other card. I suppose most people sharing a hotel room come and go at the same time, but not us. It's a nuisance.
One hotel we used to stay at used a different sort of card I've not seen elsewhere - each card actually had a sort of computer chip on it (you can see the tiny little motherboard-type-thing-y). THOSE cards were reprogrammable, worked like gold...and must have cost it, too, because there was a hefty charge for not turning them it at check out. If I can't key in a code, I'd want those.
The problem with the smart phone app is service - what if my phone doesn't get service in your area? I think this is a great option...if you're in an extremely urbanized area. And I have a backup battery for my phone LOL