line test

For trout up to about 4-5 pounds, I use 2 pound. For steelhead, I use a 6 pound base with 4 pound tippet. 4 pound is sor of a compromise if I ecpect to run into big fish.
This is spinning gear of course.

For a fly rod, I usually have my 7'6" Orvis Brook trout rod. 4wt, technically, but I re-eyed it. It will cast a 3wtfwd, 4wtfwd and 4 DT(sink or float) or 5DT (float) also. Tippet depends on the fly…usually 14-24 sized hooks for drys, or down to size ten streamers and nymphs. I also have a 6wt Ross pack rod that is OK for packing. A bit heavy, but it works for #8 streamers, large nymphs and small bass bugs. Often, I will blend this with a Childe Spinning reel for trolling in the boat or casting. A really good casting rod for lakes at 8'6"…it will cast a spinner a bloody "mile." with 4 pound. I carry an extra tip eye in case it gets worn. I have several others but I don't carry those in since I broke a couple over the years.

For bushwacking and a hard climb into some smaller water, I would siggest the 2# with some #10 and 12 hooks and maybe 5 or 6 size 16 hooks for catching small bugs and baiting your own hook. A few small bobbers works great when coupled with a 5' 2piece UL rod. Fast action graphite works pretty well.

Here is a picture of a 3-3/4 – 4 pound brook trout I caught in the rain a couple years ago on 2 pound test with a streamer. (Note the fresh hook was added after clipping the streamer off and first 20' of line. For reference,the cup measures about 3-1/2" in diameter, never bothered to really scale it. He was supper for two and a dog.):

Two pound test monofilament is all you need for trout in the Sierra, but I use four pound because it's easier to tie into knots and you don't need so much line to fill the spool.

I use 4 lb in the Sierra, because it's easier to tie knots with, as above. I use 2 lb leader, so I guess I am still fiddling with the fine stuff.

Eric, how long of a leader do you use typically?

Knot tying, that's why I have used 4 lb. line for years, the 2 lb. breaks too easily for me, trying to get that last little bit of tightness. Of course I use a fly with bubble, so no finesse with me fishing, it's an activity and food source at times.
Duane

I use 4lb. 2lb is fine. Also make sure you have your drag set so you can't break the line.

Just be a bit more careful with 2 lb …

Like Erik, I use 4lb. on the spool with 2lb. leader. The lighter leader is a little tougher for the fish to see in our crystal clear alpine waters in theory, but the main reason I use it is to minimize the lost line if I catch a snag way out in the water. A good snag that requires me to bust the line is easier to deal with when I am only losing the last few feet and my fly. A mid line break and I lose the fly, swivel, bubble and as much as 50-100+ feet of line depending on where it breaks.