Long time since I played with either, but I remember my Foundry and Harlequin ones looked fine together.
I didn't get any Steve Barber ones as I already had enough Gladiators, but I did use his spectators to populate my amphitheatre. They are quite small, and if the gladiators are the same size I think they would look pretty puny up against the others I mentioned. Didn't matter for the background crowd, though.
Don't have any of the others you mentioned.