While all the above advice is sound, I will be the voice of reason. I began fly fishing as a youth and my first "real" fly rod (ie: not a $20 fiberglass pole from Canadian Tire) was a 4 piece 6wt dragonfly rod. I fished this rod for everything from trout and bass in lakes to salmon and steelhead in rivers. I was able to land every fish I hooked without breaking the rod (although I did snap off a few large male chum that proved too stubborn to come to hand quickly), and not one of them appeared over tired (still had plenty of fight) as I released it. While an 8wt allows you to muscle in fish for release more quickly (so it is better for the fish), if you do not have the means (and I did not either) to have the luxury of multiple rods for multiple prey, a six weight rod is the most versatile option, not too heavy for any but the smallest trout, and not too light for any but the largest salmon. However, be sure to pair with a reel with a decent drag as that will ensure if you do hook a large coho or chum, that you can tire it out on the reel, as opposed to trying to haul it in with the rod. You can also help yourself by not fishing fast heavy water (not the best for fly fishing anyway), and sticking to slower slack water for coho. Also, use a lighter leader (I used the weight test of the average size fish I planned on hooking ie: 6 pound for coho), so that you can break off a big fish that either is too big for the rod or that gets into that faster current. Better to leave them with a small fly in the jaw than tiring them too much trying to get them in, especially if you have to release it. When you can afford it, go ahead and expand your arsenal with an 8 wt (I use one now for all salmon and steelhead for all the above stated reasons) and a 5 or even 4wt for smaller trout (I still use my 6 wt dragonfly).