I like Pezhetairoi the best, probably.

Good looking, efficient, dependable, and not-too-expensive, they form a solid battle line to pin the enemy down with.

Of course, the elite ones are better 1v1, but they're usually also awfully expensive, and due to the fact that I usually start building a new army always when I get enough incomes I never get enough income to build elite-armies.

While I understand the pro's of the cheap levy-phalanxes, they usually suffer more losses, can't be trusted as well, and, well, (vanity FTW) they usually don't look that good, and thus be unfit for ze Imperial Legions.

So, I'm gonna go with Pezhetairoi.