If one has LT *G, then any better status on an alternative program will mean you need to fly that carrier. *G is the presently the high cross-carrier status (although there has been talking in *A about a high alliance wide status). So for status benefits pick the carrier you will fly the most.

For RDM benefits, it gets more complex. There is the earning rate and there is more variation especially for deep discount fare with other programs (effectively Similiar to UA PQD multipler approach).
Then there is redemption available, again this matters what carrier you wish to use for award flights as most programs provide better access to their native program. (aka no XN or the rare IN for non-UA elites - similar for other carriers)
And there are fuel surcharges, some carriers have hefty cash requirements for awards (especially for partner flights).

For upgrades -- you are generally restricted to your home program except to top fares (UA GPUs on LH/NH/CM are an exception)

And advance preferred economy seating to generally restricted to the carriers' elites. (aka UA E+)

Maybe overly simplified, but status above *G is not very useful unless you are flying the carrier you have status with.

And what fares you purchase will matter if status is of any benefit.

And finally, *A carriers generally will not status match another *A program's status.