As with the majority of my legacy figures "all" * are mounted on either 20 mm round (for Litko movement tray - 20 mm circular openings - and "trayless" skirmish games) or .75" square bases for forming units for non-skirmish games when I don't have enough Litko unit/skirmish movement trays with the appropriate square openings.
I would say anything works as long as you are consistent.
Preferably your opponents use the same relative basing conventions.
Gracias,
Glenn
* I
do have some fantasy/SF/historical figures on larger bases (came that way, such as Reaper, or the size of the figure is too large to fit on a 20 mm/ .75" base.) I just try and avoid that with new purchases.