I really hate to disagree with Samonela's recommendation of Maxima Ultragreen but it's way down my list for use with spinning reels. Don't get me wrong, it's excellent monofilament and it's my number one choice for leader material unless I'm using fluorocarbon.
I'm sorry I wasn't clear in my earlier posts.
If you re-read you'll see that I said that I find Maxima too wirey for spinning reels in my experience, if I choose to use mono for a baitcaster however, it is my first choice.
It is hands down my favorite mono for leaders.
Maxima Ultra Green has proven it's quality over and over to me, I once landed a 38lb King Salmon on a 10 lb UG leader with a tiny #6 Gamakatsu hook, in a fast moving riffle while targeting steelhead.
12 & 15# Ultra Green is my favorite for salmon up to 40lbs, I'll use 8 & 10lb for most steelhead fishing, where I fish they run up to 20lbs, often water conditions dictate line weight.
Monofiliment has different qualities for different applications, very light line becomes important in low clear water conditions as well.
Light line slices through water at a much quicker rate than heavier gauge line which is more bouyant with it's larger diameter, this can often mean the difference between success and failure when fishing for bottom hugging salmon or steelhead as lighter lines will drop your presentation down to the strike zone where the fish is laying on the bottom of the stream instead of floating over the top where they might not be interested in your offering.
I use Power Pro Braid for my main line, it's sensitivity, small line diameter, lack of stretch and superior strength are unmatched and give you definite advantages over mono in MANY circumstances, I always use a mono leader when fishing braid for a number of reasons.
I'll use a clinch knot on swivels and a snell knot or egg loop on hooks, the quality of your knot is incredibly important on big fish as knot failure is a leading cause of heartache when guys hook "The Big One".
I also prefer baitcasting reels in most of my fishing situations, they offer much more control and less line twist than spinning reels and their drag systems are much smoother in most cases which is also very important when fighting big strong fish.
There is however times when a light spinning rig is optimal, such as when targeting smaller fish or when in tight quarters using very light baits or artificials, I usually load the spinning reel with a very limp selection of Silver Thread, it is a high quality mono and a great choice for spinner fishing, but not nearly as abrasion resistant as ultra green, seems you can't have it all.
None of my opinions are to be taken as "The Only Way", but they are what have been fire tested over several decades and hundreds of big fish and it's what works for me.