1k sons are great, 4+ invuln, Hellfire Bolts (ap 3 bolters) and ALWAYS shoot 24'. Downside? speed, they're slow and purposeful, but rhinos fix that. Could incorporate a termie squad with MoT, 4+ invuln termies. And Ahriman is awesome, either 9 str 4 ap3 range 18 BS5 doom bolts, or 3 str 8 ap1 range 24 BS5 Bolts of Change. Or 3 attempts at changing that pesky special char into a chaos spawn ( which could be fairly easy, seeing as the test only requires you to roll and match targets strength) OR Demon Prince with wings, MoT,and Warptime for like ...what.....150 pts? maybe 160, i hate chaos and their dirt cheap demon princes. Toss in some Obliterators and your pretty much set.
Death Wing....My friend's dad runs these guys, and with the new marine dex, they're tough. 2 Land Raiders, Belial, Termie Chaplain, and 4 Termie Squads, each specializing in a different area. He has barely any models, but two squads are in those land raiders, the other two DS, you won't be killing those Land raiders :p.
So all in all both armies are pretty tough, seeing as all your models wiill have an invlun save, whether it be your 4+ on 1ksons, or 5+ (3+ invuln if you take shields) on your termies. Both need transports to get them where they need to be. And heavy support shouldn't be a problem for either, because they both are marines and marines do pretty nicely with Heavy Support. So it depends on which kind of tough do you want, and if you want to spend your time assaulting, or rapid firing ap 3 bolter death :p