Having a bit of a debate with my friend over this. Seems silly but...
I don't often block people's numbers as it means their number is actually still in my phone (WhatsApp) which can cause more temptation.
I just delete their number. If they continue to text when asked to leave alone I block.
My friend just blocks everyone that she doesn't want to speak to again.
Sounds silly, but what do you find easier to do. - I'm meaning ex's