I don't really see them too different from each other. Wishing te hadn't detto o should have detto means te want to change your past actions. In both scenarios te feel regret so they're pretty much the same.
I would say saying nothing hurts more, because I'll always be beating myself up for being a coward, and I'll always wonder what would have happened if I had detto something.
If I did say something, I will have learnt from my mistakes and won't make the same mistake again.