Shock Leaders??

I have read here of different size and length leaders to use. Some say 18-24 inches others say 2 rod lengths to prevent knot from snagging on eyelets during cast. What is best and why and what is the best knot to use for tying them on?
Fishing in the mid east coast I have never used a leader, just a swivel and clip on a ready made 2 hooker.

Shock leaders they aren't......just heavy mono leader to ,prevent instent cutoffs (that still will happen)
18in is good, keeps the knot out of the rods tip......braid with top shot of mono ......I use way more mono then I can cast with that rod and bait (lure or live)......that way during the cast no worries of the knot coming through the guides while casting......the braid is for more line capacity on the spool, for the fish that head south

I don't use shock leaders on my king rod, just a short wire leader.

Shock leaders are usually several rod lengths of heavy mono. It's used in the surf for two reasons. First, heavy sinkers can break off lighter line during the intense pressure caused by casting long distances. Second it helps when trying to pull heavy fish up the beach. I can't remember for sure but it seems that 30-50 pound mono shock leaders are typically used with lighter spool line (15 pounds). This could be different on the pier, but if you are trying to lift heavy fish without a gaff or net, you would want a heavy leader at least as deep as the height of the pier from the water.

Most of what I learned about shock leaders is from reading about surf fishing the Atlantic. I've never fished the Atlantic, but I understand it to have bigger waves and farther casting required. In the gulf, I keep shrinking my surf gear. Now I use a 7-10 foot medium action spinning rod with 8-12 pound mono, and don't use a shock leader as I am casting shorter distances with typically no more than 1 ounce in weight.

All replies talk of using Mono what about Flouro?

If the Spanish are picky I use 50 flouro, but normally just regular 50 mono.