Collies make good guard dogs, not good protection dogs
Before you take up protection dog training I hope you will accurately assess the hours upon hours you will invest in training, and the loving bond you will develop with your dog(s).
When faced with a deadly situation will you then be willing and able to send your dog to defend you till its' death?
I personally went thru this self examination and decided I wouldn't give up my dog to a gun or knife weilding BG. Consequently, I chose a Collie. Why? Because Collies are great guard dogs: they bark and they bark alot. Mine will bark loud enough and early enough for me to jack a 45 acp into my 1911 and introduce the intruder(s) to REAL deadly force. Nothing else succeeds so sufficiently as the 45 acp.
German Shepherds, Dutch Shepherds and Belgians are all great protection dogs(as a group, not individually). These breeds have all been battle-tested and proven their value over and over. Any other breed you're taking a 50/50 chance on.
A couple of Collies and a bunch of GSD's have allowed me to sleep in comfort and safety for the past 45 years.
Good luck with your choices.