I always use the tz version, except when I forget.
I find it nearly impossible for me to forget how this works. But that is probably because I just pretend that the standard, multi-word, data types don't even exist. It's not that "timestamp" defaults to "WITHOUT TIME ZONE" but rather that there are only two types in existence: timestamp and timestamptz. It's self-evident which one doesn't handle time zones.
Suspect that it is extremely rare when one would not want to use the TZ option, which suggests to me that using TZ should be the default.
I would agree, but at this point I'd leave it up to documentation and educational materials to teach/encourage, not runtime behaviors.