Q: mag safe  which one

The 85W adapter will work with all of them. They're all the same price.

Lower powered models will also work with all of them, but may not have enough power to operate the Mac and charge the battery at the same time. If size is not a concern get the 85W model.

In case you're interested the following adapters will suffice for these respective Macs:

45W: MacBook Air only

60W: MacBook Air and MacBook Pro 13"

85W: Everything

Read this.  http://support.apple.com/kb/HT2346

Newer MacBook Airs and Retina MacBook Pros use the MagSafe2 connector. Earlier models use the MagSafe connector.

If it fits, it will work, but detemine what you have before you buy a power adapter.

MagSafe 2 came out in 2012 so it won't fit any MacBooks which were discontinued in 2010.