Using Migration Asst, have gone from Mac 1 to Mac 2, but now Mac 2 back to Mac 1? I had to send MacBook Pro #1 out for repair and used Migration Assistant to temporarily work on a loaner (MacBook Pro #2).

Now #1 is back. Do I:


Use M.A. to go from #2 to #1, hoping it magically merges and resolves the differences in my user account existing on #1?
Reformat and reinstall the OS on #1, and use M.A. to go from #2 to #1?
Some other optimal solution?
Assuming that you did a full migration from MBP #1 to MBP #2, then I'd probably go with your second option (although that may depend on how long MBP #1 was away for and how much work you've done since).

The only downside of this approach is that some 3rd party software may need you to reactivate them in order to use them. It's not really a problem, just may add a little inconvenience if you happen to be in that situation.

Since you asked, there are indeed other solutions, such as cloning the drive from MBP #2 to MBP #1 using software such as Carbon Copy Cloner or SuperDuper! You can also use Disk Utility to do the same thing.