Was about to chip in. Actually the last game I played was an EA planetery assault vs Dilgar at Battle level.
Actually the nastiest I found were Chronos, theyre cheap and have masses of heavy pulse cannons and railguns that can make mincemeat of emplacements. The marathon put the hurt down pretty nicely too

. T-Bolts were usefull too

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The real star were the Chronos they pounded the hell out of the planet and whats more they carry quite alot of troops too, (and along with an Assault hyperion) landed as much as they could as quickly as they could and took the planet after a preliminary couple of turns bombing to soften it up

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Oh and yes, I know I say Chronos are the answer to life the universe and everything when playing Crusade EA but, well... THEY ARE!!!