Variable for the ease of locating targets.
Fixed is convenient for not worrying about focal plane, it usually has better glass for less money (cheaper to manu) and of course the "cost factor".
I find most of my lower power variables stay on the highest power all the time.
A fixed 4 is a great lever gun scope.
I like higher power for target identification and accurate neck shots.
Bench banging steel at know distance the straight 10 should get the job done.
Both have their advantages, it's a tool, pick the right one for the job.
The fixed is a box end wrench, the variable is a Crescent.