What troops to replace Royal Snakes?

[Roman]

I have been using Royal Snakes almost from the beginning of the game (pretty much as soon as they were available). Being at level 15 now and with supplies gradually starting to diminish, I wonder what troops I should use to replace them? Royal Snakes are just amazing - they don't have high leadership requirements, they have respectable hit points and other statistics, their attacks don't elicit retaliation, their "Lunge" ability is useful, they are immune to poison and they are are venomous. What's not to like? I have 'upgraded' all my other troops though (apart from Bowmen, but I will probably start using Elves/Hunters soon), and rotated others, some even several times, so I am wondering if I am missing something - some great replacement for Royal Snakes. Or are Royal Snakes going to rule the battlefield until the end of the game?

I should note that the supplies are nowhere near critically low yet (a considerable number of resupplies is still possible), but I am thinking ahead, as I have recently been venturing into higher-level areas than I probably should be and the rate of losses has, of course, increased in these places.