At the moment I'm torn between Aventine, Black Tree Design and Foundry. They all have models I like more and models I like less, difficult choice
Aventine offers first-class service, and they may even let you pick just the models you want from a given pack. Also, casts are always crisp and clean, so highly recommended.
In contrast, BTD is rather hit and miss in that regard. Also, their Early Imperial Roman range looks a bit dated in comparison to, say, Aventine. They are also noticeably bigger than Foundry miniatures for the same period (maybe apart from Steve Saleh's clone trooper sculpts). Thus, Aventine and Foundry won't match either.
Despite the scale issue, for nitpickers, the ranges also cover slightly different periods: Aventine has a focus on mid to late 2nd century CE, while Foundry (both Perry and Saleh sculpts) covers the late 1st to early 2nd century, and BTD is rather generic 1st century.
If you're still on the 'Caesarian' track, it should be Foundry all the way.