Any advice for making a set for this guy?

I was considering
Aggron @ Aggronite
252Hp/252SpD/4Def
Sassy
Rest
Sleep Talk
Curse
Iron Head/Heavy Slam

I'm struggling to pick between Iron Head an Heavy Slam, the former is more reliable and has more PP, which is good on RestTalk sets. But the latter will completely crush anything small that comes in.

Any suggestions or other good sets I could run with Mega Aggron?