There's no single leader that is ideal for all situations, but with minor changes you can have a leader that comes close.

Trout are easily spooked, right? So I'll need a delicate leader for such purposes. This is a common thought process shared by many anglers and manufacturers, but it has it's limits. I'm going to recommend you do the complete opposite and get a stout leader. Trout are spooky part of the time, but they can also be quite aggressive. They often chase down and devour good sized prey, even on small creeks. Sometimes the smallest of flies is in order and sometimes large streamers are the choice of the day. A person can unknowingly limit themselves by sticking to small flies and light leaders. If you like to adapt as you go and seek more variety in your fishing, a versatile leader is what you'll need.

You'll find a variety of prepackaged trout leaders. Unfortunately most are too light to cast big or heavy flies well. You also may have seen detailed formulas for the ideal homemade dry fly, nymph, or streamer leader. Here's a single simple leader that works well for a variety of situations.

This is the typical leader that I use on my 4 weight fly rod. Start out by buying a stout commercial tapered leader. This is much easier than having to tie a lot of knots when constructing your own. I'll use around a 7.5ft leader tapering down to around 10lb test. Often labeled as a bass leader. It has a large butt diameter that will turn over large flies and will do well in turning over a long fine tippet section when fishing spooky trout. This stout leader is a good foundation for your nymph and dry fly leaders. For such a stout leader you'll want to cut back the front taper of your fly line to better match the leader. Here again most "trout" lines have too delicate of a front taper (For and explanation read my post from a couple weeks ago about preparing a fly line for fishing).

Next tie onto the leader a 1 to 2ft mid section that will be the transition to your tippet. For me this is usually around size 6-8lb test. All you need to do is add a length of tippet to match your fly. Something a little larger for weighted nymphs and something smaller for dry flies. My typical leader is around 12ft long. If you want something shorter cut some off the butt of the leader. If you want something longer get a longer leader for the foundation, add a longer mid section, or make the tippet longer.

This system will make it easy to change from a short stout streamer rig to a fine dry fly rig and everything in between. Just cut off the mid section and tippet and stick it in your pocket or waders for streamer fishing. Tie it back on to fish nymphs and dry flies. Much easier than changing out the whole leader. Simple and versatile.