If you mean "stronger" as in more dramatic or passionate or more emotional, I think that suicide would be stronger. When you murder someone, you're hurting someone else, but to commit suicide, you'd have to overcome all your rational thought and put yourself through a lot of pain (mattering on how you did it). Guilt might hurt a lot, but when you murder someone at least there is a tomorrow to look forward to.

Both are equally as final and hurtful to the victim's loved ones. But suicide leaves the family feeling guilty - they feel they could have prevented it. So, emotionally, suicide leaves a bigger scar!