Unless you fly a heck of a lot and expect to keep doing that for a while, lifetime status on UA (a million real "BIS" flight miles) is a long way off. Until then, UA annual status is a year-to-year thing, no "soft landing" just one level down if you miss.

If you want *A status for things like lounge benefits, there are easier airlines to get it with than UA. The current favorite seems to be Aegean. Those will get you into UA's RCCs in the States, which UA status won't, but they won't get you into E+, which UA's status will.

You never said what your current total is but if I were about a million AA lifetime miles down from where I am now and considering this question, I'd go for the AA bit.

(Regarding baggage handling: I usually get Priority tags when traveling with my wife - by myself, I never check a bag - but it doesn't seem to make much difference. It's not like all the bags with those tags come out first.)