The short answer is the Palomar Knot, but I suggest you keep reading. We have over a dozen knots on this site just for tying on terminal tackle. The Knot Cards we sell have from 3 to 6 terminal tackle knots. So, why all these knots if you only need a Palomar?
OK, let's talk about the Palomar. Pros: Easy to tie, easy to remember, it is one of the few knots that works well in all materials (mono, fluoro and braid), works in a Drop Shot Rig, and STRONG. This knot is one of the top 3 terminal tackle knots in terms of reliability, if not the top knot, depending on the test. It will not fail you. Cons: It takes more line to tie, which can be an issue if tying a fly onto tapered leader, hard to thread the line two times through very small hook eyes.
The point about the Palomar then is that is can be your one best, go-to knot, but because of just those two “cons”, you need to know more knots. Now, if you are only trying to overcome the two cons, I’d suggest the Uni Knot, but now we are up to two knots you need to know, not a “one and only”. So, should the Uni be your “one and only”? Pros of the Uni Knot: Easy to tie, especially for bad eyes and/or low light situations, relatively strong. Cons: Doesn’t work in braid and it is not the strongest knot out there. Why would I recommend it? Because it is easy to tie and it is strong enough.
I know, there are those of you that are testing knots in their garage and reading up on Knot Wars type testing, etc and a statement like "strong enough" might be too ambiguous for you. Here’s what I mean by strong enough. In most cases, a fish that is lost during battle is lost for reasons other than a properly tied knot. Note I said properly tied because even the best knot tied wrong or poorly will fail. Here are some ways that will lose a fish before a knot fails: The fish throws the hook (or lure), not a good hook set and the hook pulls out of the flesh of the fish’s mouth, the line abrades at the fish mouth and breaks above the hook, (this is a good reason to always check your line after catching a fish and make sure it is still smooth and good - retie if not), the fish takes you down and saws you off in structure (rocks, timber, etc.), a light wire hook straightens during a long battle, the line itself is old and just breaks. If you tie any fishing knot correctly, have good line and the drag set on your reel correctly, you will lose a fish for any of the above reasons before you’ll suffer a lost fish due to the knot, especially a well tied Uni Knot.
The point is, outside of specialty knots, which I will cover in a future blog, you will do fine with the Uni Knot or the Palomar Knot. Pick a knot that is easy for you to learn, easy for you to remember and to tie, then tie it correctly. If you lose a fish odds are it won’t be because of the knot. By the way, I am fully aware that many knots “test” stronger than the Uni, but I can quickly tie it correctly, in the dark with cold hands so it is my go-to knot. You might prefer another knot, maybe a technically stronger knot. Just learn it and love it and trust it. The fish will always find other ways to get off your hook!