HDF would be appropriate if you're emulating the goofy parody movie, but if you want to stay true to the original book, you'd use Brothers units, because their power armor fits the Mobile Infantry much much closer. They're called "Mobile Infantry" because the armor lets you run as fast as a car, and carry weapons sized for a tank.
Here's a quote from the book describing the armor.
A suit isn't a space suit - although it can serve as one. it is not primarily armor - although the Knights of the Round Table were not armored as well as we are. It isn't a tank - but a single M.I. [Mobile Infantry] private could take on a squadron of those things and knock them off unassisted...
...Suited up, you look like a big steel gorilla, armed with gorilla-sized weapons.
The real genius in the design is that you don't have to control the suit; you just wear it, like your clothes, like skin.
The secret lies in negative feedback and amplification.
This anime adaptation is probably the most book-accurate depiction of the mobile infantry:
I would love to see custom lists for Starship Troopers (not just generic HDF and Alien Hives). I enjoy watching the movie, and the book is one of Heinlein's best.
I used to have the Avalon Hill version of Starship Troopers. I would also love to see lists based on that game as well (Battle Brothers with nuke launchers sounds awesome). If I ever finish painting minis, I might try to make some lists as well.