There are at least 3 types of all rounders.
True all rounders. These tend to be the can be selected as either batsman or bowler type, but generally not "great" at either.
Miller, Botham, Stokes or in modern equivalent Jadaja, Holder etc.
The batting all rounders. Self explanatory.
Sobers, Kallis, Hammond, Simpson
And likewise self explanatory the bowling all rounders.
Hadlee, Imran, Pollock, Davidson etc..
And I don't think it fair or even possible to compare the different types. Miller being, at least in an ATG conversation would be rated more genuine all rounder, though for his team would possibly be classified as a batting one. But you can't compare his contributions to say a Hadlee or even an Imran because they performed different roles and filled different responsibilities.
If we look beyond the all rounder discussion and just look at them as cricketers, they were and all invaluable to their teams.
Imran was a great bowler who could hold up an end and provide a partnership with a top order batsman or hang on with the tail to save a game and he also captained the team.
Sobers and Kallis were worth their weight in gold. great batsmen, handy 5th bowlers who even came on 1st change or in Sobers case often opened the bowling. At times wining the game for their teams with the ball by breaking partnerships or taking 5 wicker hauls. And in the field, you can't watch highlights of Steyn without seeing Kallis holding some stunners at 2nd. Sobers was brilliant everywhere and alsosublime in the cordon.
If I was building a test team from scratch, they would be among the 5 names I would legitimately consider for the 1st pick. Well either Kallis or Gilly for the 5th.