I wouldn't recommend the AC (unless you desperately want cheap Marriott credits). It's quite a rundown hotel (at least back in 2021) and the location isn't the best.

There are a lot of public buses in Penang (one that runs from the airport to George Town) but I don't know if it goes via AC (google maps is pretty good with public transit in Penang). Or else, you can take Grab (SE Asia's version of Uber) - much cheaper than Grab in KL. You can also get a e-hailing via the Air Asia App (they have e-hailing services in Malaysia as well). There will be a train connecting the airport to George Town and beyond but construction hasn't even started yet - so don't expect to see it until 2030 at the very earliest.