Welcome to the Strelets Forum. Please feel free to discuss any aspect of 1/72 scale plastic figures, not simply Strelets. If you have any questions about our products then we will answer them here.
Normally I would buy all of the sets for a subject I like, but since you asked
Vikings: Orion (I like the Strelets set)
Norman:Revell
Saxons:Revell (Strelets is my favorite)
Knights/Crusaders:Italeri
Conquistadors:If the scale is compatable, both
Swedish:Streletes
Streletes Artilery
ACTA British Infantry 1775
Italeri French Infantry
Zvezda Imperial Guard
ESCI Union Infantry or Italeri Union Infantry
Same for the south
Atlantic Egyptian Infantry and Cavalry (reissued by Nexuss Games)
I think that most collectors would buy both every time. If you can get hold of them and they are compatible in size then mixing various manufacturers generally gives a much better representation. Look at the Plasticsoldierreview web site and you can see the figures and decide for yourself.