Stone Edge easily.
Thrash is unfortunatly a horrible move. It may have similar effects to the popular Outrage, but it's Normal type hinders the move and means it provides no coverage whatsoever. And becoming locked into such a move means the opponent gets a free switch in to a Ghost type as well, which later leaves you confused. Stone Edge is a much better choice, as it is STAB this time and has a nifty high critical-hit ratio.
Only use Thrash if you have no better option to use.