For me, I'd say NONE of the ones listed. Why? Space Marines of the WH40K setting pretty much beat out any suggestion of any other Sci Fi infantry, with the possible exception of the original Sci-Fi soldiers, the Mobile Infantry from Robert A. Hemline's Starship Troopers novel (y'know, the guys with Battlesuits and friggin' Atom Bombs wielded to them!)
Anyways, your average Space Marine is modified to an extent where he can shrug off just about any injury outside his armour, hibernate in the Vaccum of Space for extended periods, and even absorb your thoughts and memories by way of eating your brain. And this is WITHOUT the use of their Patterned Power Armour.
Speaking of, standard Power Armour is essentially motorised tank plates slapped over them. Considering they have the ability to shrug off most injuries beforehand, with the armour they can be pretty difficult to take down without the correct weaponary. And then let's not forget their standard weapon - the Boltgun - is essentially a Rapid Fire, Armour Piercing Grenade Launcher that fires fist sized explosives at you.
Yes, 40K has a habit of turning everything up to eleven. While Guard also have plenty of brass balls and up to Eleven weapons (Leman Russ Tank, Deathstrike Missile, Marbo etc), they are at the end of the day Redshirts unfortunately. But hey, I suppose it beats being one of the poor guys on PDF Duty.