How to avoid the 737 Max? Fly only airlines that don’t have it. Luckily there are still a few around in Europe. Since the two fatal crashes I have avoided doing flights with 737s.
In the US, Delta seems to fly a lot of Airbus but unfortunately this is fast changing too based on their recent-ish large Boeing orders.
Virgin America had an all-Airbus fleet...until Alaska bought them and ditched the Airbus leases because 'Merica-Seattle-Boeing or something. (I'm sure they justified it as mechanical/maintenance efficiencies from operating a single type, but they made a bad mistake staying all-in on a failing company's product.)
Delta's famously agnostic - they fly whatever is net cheapest for them, even if it's an old airframe (that they own outright) that sucks fuel (rather than a more fuel-efficient plane that they lease). Boeings got cheap after the MAX problems. On the plus side, Delta is a very well run operation with competent maintenance.
And then there's Southwest. All Boeing, bad maintenance history. A culture that hates change and new technology.