Best 9mm Mouse Gun? What's your opinion?
"Best" is a very subjective term.
"Mouse gun" is another subjective phrase.
I'm a huge fan of sub-compact 9mm "pocket guns"
My all time favorite, simply because of the badassedness of it is the Rohrbaugh R9
While the R9 is incredibly small, it suffers from limited capacity.
The Sig Sauer P290 is another personal favorite because of its accuracy and concealability.
If you're looking for an excellent pocket 9 on a budget, you should definitely check out the excellent SCCY CPX2.
The CPX-2 gives you a light weight pocket 9 with a 10 round capacity. It is almost an exact clone of the Keltec P11, except the quality, workmanship, accuracy and price are better.
I bought mine for $250 and it is a constant companion, when it's "legally allowed" to be.