Big hair- 42mm or 50mm?

[Spookey80]

Am just about to purchase a babyliss big hair, when two have come up 42 mm or 50 mm barrel, I didn't realise there was a choice.
Which one do I want?
I have mid length medium thickness hair.

Thansk

Bump- anyone?

I have shoulder length, thick hair and use the 42mm one. It's fab - think I would find the bigger one a bit too unwieldy, but not tried it so don't know for sure. If yours is longer than shoulder then the bigger one might be better.