Which is worse straightenig or curling?

any ideas?

They are both equaly damaging. The trick is to buy professional quality tools and quality hair products. For any kind of heat styling routine, you need to have a protein/deep conditioning regimen and use a good heat protection product. Redken Heat Glide is awesome.

I also recommend Simply Stylin' Silk for heat protection.  Unlike other silicone-based heat protectants, it's pure silicone with no fillers.  So just a little bit can be way more effective in protecting the hair.