The Pentapods.
The Hivers, I feel I understand; in fact, there's a fair bit about their outlook that vaguely maps on to my own, at a stretch. It's one of the reasons why, despite the K'kree being my favourite faction, the Hivers are the one I probably sympathise with most. They're alien, but there's overlap that allows for subtle common ground. (They are, after all, the product of human minds like any fictional aliens).
The Pentapods, though, I can't say I understand because I don't think they're supposed to be understood, even (or especially) when the Big Basic Secret is revealed. I'm not sure if anything about Pentapod psychology is supposed to be compatible with Human. By which I mean, because all fictional aliens are human-created, the way to make them truly, fully alien (if such a thing is possible, assuming consciousness doesn't come with certain universals) is to give only questions, never implied answers.
Hivers and Humans are definitely able to understand one another if they put their mind to it -- or at least substitute familiar ideas that sort of map onto what the other race experiences. After all, Hivers are playable. Playable Pentapods would defeat the purpose of Pentapods.