I like Osprey, too, though I only have their books on the 18th century armies, no ancients, so I can't speak to the accuracy of that specific range.
Same goes for Funcken. I've got Funcken books on 18th century armies. They have good text (albeit in French, which I can read, slowly), and the illustrations are pretty good. But I think they've since been overtaken by newer authors and titles.
I do recommend visiting Berliner Zinnfiguren's website, www.zinnfigur.com, and browsing their Books catalog. There has been a lot of content published on the ancients in the past 10 years or so, especially on the Romans, and the Germans love that subject. You might find some books there that will prove useful.
Hope that helps!
Best regards,
Brad