An Imperial Knight Paladin excels in engagements, where its Chainsword and Shock Lance will make short work of most targets. It is also armed with a Battlecannon for long range support.
Champions of Chaos are supremme warriors armed with powerful weapons touched by Daemons. They aid also the summoning of Daemons to the battlefield.
Berzerkers are frenzied close combat monsters who will likely tear apart most oppenents they get to grips with. They have good armour and will not break or flee when the going gets tough.
The Space Marine Battle Barge can launch an enormous Orbital Bombardment in the latter stages of a game. It also allows formations to planet fall via Drop Pods, Thunderhawks, or Landing Craft, though a Strike Cruiser has the same capability and is cheaper.