Apple iphone users: Do you use iMessage or turn it off and use regular SMS texting?

Apple iphone users: Do you use iMessage or turn it off and use regular SMS texting?

IMessage since SMS texting gives additional charges.

I always leave it on, most that I message have imessage so I use a cheaper text plan since its free, and if leaving on others can send free if they use imessage.

I use regular SMS texting