Peltastai are great light infantry, I find. Once they've used all their javelins they can usually be used as main line reinforcements if you absolutely need them. Akontistai, on the other hand, are just about useless once their javelins are used. Thureophoroi are also good choices, but remember that their javelins are precursor weapons, meaning they will charge after you order them to throw them. If you don't want them to do that, just order them to Fire At Will or just order them to attack an enemy then hit backspace after they've thrown the javelins. As an added bonus, Thureophoroi have spears as their secondary weapons, making them excellent emergency anti-cavalry troops.