What would you find in a planetary assault force?

[Mako]

Actually, on the overwhelming orbital bombardment issue, I'm not so sure.

You still have to gain superiority of force with that.  There are lots of cases in history where naval vessels could not gain superiority over fixed defenses, so needed to land their troops away from those areas, to avoid being shot up/sunk.  I imagine the same applies to orbital combat, and probably even more so if the planet has armed defense satellites protecting it.

For me, it's a mix of Grav Tanks, Drop Troops, Drop Ships, infantry and heavy vehicles landed by shuttles, dropships, and larger landing craft/ships, orbital bombardments, spacefighters with atmospheric capabilities, etc.

Whenever possible, troops and forces will be landed away from strongly defended areas, and then moved in overland to the attack, but in some cases, they may also need to land in hot zones, due to: the value of the target; urgency in completing an operation; chance of enemy reinforcements showing up from on the planet, in the solar system, or from nearby stellar regions; etc.

In some cases, the Grav Tanks and IFV's/APC's may drop in on the planet independently, from orbit (like swimming tanks and LVT's in WWII), and in other cases they will be brought down to the planet's surface for offloading there, by other vessels.