I only found Lusotannan and Sweboz satisfactory, though I haven't seen much east of the Aegean yet.

Carthage was sometimes decent, sometimes not. They fielded near-100% militia stacks on the islands (probably couldn't recruit much else there), but their last army in Africa and their Iberian army were both pretty sensible. Could have used more cavalry and missile units, but it's hard to argue with an army consisting mostly of outstanding infantry (though one could argue that the units derived from Rome's Polybian units shouldn't be fighting Camillan Romans - short of introducing Punic reforms there's no way around that, though).

Celts - their armies are utter nonsense. I've posted before about the Lugoae/Iosatae armies, 50/50 split. Most towns can't build any other units in my game. As long as they keep fighting each other the slinger spam won't be a direct problem, at least.

Epirus - also slinger-spam nonsense. And many of the units who aren't slingers are archers.

KH - levy hoplite hordes, though they do spit out the occasional quality unit for variety.

Makedon - hard to tell, what troops they have are constantly ground down by KH. They could be OK if they ever had the time and money to recover, which I don't expect to see in my current game.

What I've seen of Ptolemaioi thus far hasn't been very sensible. One stack was 100% heavy infantry, mostly intact units. No cavalry or missile units at all, so they were easily demolished by a force of mercs and a partial legion, heavily reinforced with extra missile units and cavalry. Mmm, peltasts and numidian cavalry vs. phalanxes, tasty! Their next stack looked Macedonian - in the sense of being 17 badly mauled high experience remnant units. Doesn't much matter what the units are if they're that badly understrength.