The horns are too chaotic for SM, IMHO.Why don't you try the hornless Chaos helms instead.
I think the marine's heads look better if you want to fit your theme. But if let's say you wanna use the chaos heads then I also think it will fit the dinosaur theme.Though I would say those horn heads will give you more chance to paint on the dinosaur feel.
The 1st one look better. They do look much better than marine ones.
May be you just magnetise the head, so you can have marine helmet when you play Dragon marine, and use the fantasy chaos helmet if you play chaos or daemon army, further more, in future if you found a good looking head you can swap as well! Hehe.