I use both to great success in my list. 2 Daemon princes, greater daemon, 3 plague marine squads with 2 melta in 2 of them, 1 plasma in the other. the plasma champ has a powerfist, the others a champ with meltabombs - all in rhinoes with possessed and havoc launcher, 2 squads of 5 lesser daemons to hang back once they come on board and 6 obliterators 3x2 to top it all off.
3 Monstrous creatures does put your opponent off, especially if the third comes in on a later point through something that previously looked harmless.