They actually have three, there's Opera, Opera Mini and Opera Touch.
Opera is their conventional mobile browser. It has special features such as data savings, ad blocking and night mode.
Opera Mini is a lighter weight browser with focus on efficiency and compression for faster loading and data savings.
Opera Touch is designed to be easy to use one handed and it can link to your desktop browser which lets you share tabs and files between Opera Touch and Opera Desktop.
Just get them all and try each out for a week or so. I prefer Touch, personally