Raiding is fine until the enemy has weapons that will shred your marines. You want to use attack so you deploy vehicles, and those eat up more hits before your infantry does.
I've raided into an Extreme Ork presence and almost been cut down the first attack because of it.
So I basically I raid to deal with anything Enemy Troop Strength 4, attack for anything more. And either way, with those numbers, you're taking casualties.
This brings up a good point, though... currently Raiding lets you face less enemies, but it also lets you bring fewer allies. It also starts you closer to the enemy, but depending on who you are facing that can be good or bad, so lets ignore that factor.
However, if you min/max your chapter with melee fighting and ambush, with the right equipment, you can routinly destroy extreme presence's with a raid, easily. Plus vehicles are expensive. So I think that the ability to face less enemies and do more damage is a little unbalanced.
Ideally, in my mind, the system choices should be reorganized as thus (And I only keep making suggestions because I love this game):
Land: Lands your troops on the planet. This is just a shortcut to manually unloading all your marines from the other view. Landed marines can be ordered to Attack or Defend.
Raid: Launches a raid against the enemy. You face less enemies, but have less impact on their forces. You start closer to the enemy as well. Also, there needs to be a perk that lets you bring vehicles on raids (Bike raid!)
Bombard: Bombard ze enemy. You should be able to choose from precision strikes and carpet bombing. Precision strikes does far less damage but also does less damage to the local population. Requires marines to be landed on the planet to act as scouts.
Purge: Purge guys.
Build: Build options, like building more defenses instead of the weird button randomly underneath the defense. There are also evidently options to build on a dead world (Never got around to trying that).
Those options should always be visible, maybe only Greyed out if you arn't able to do some of them, because I think it's confusing otherwise.
Man, how hard would it be to port it over to a better engine, like Unity or something? Or would it just not be worth it? I feel like the game is going to rapidly become too complicated for the current engine (Game maker, right?)