Ever had any trouble picking which set of strings you should use? Have you ever wondered whats the big difference anyway? Do you already have a favourite set of strings and come hell or high water, never going to change? My friend Scott has a saying that applies especially to musicians. He says "We like what we like, the way we like it, because we like it". Our (sometimes unfounded) bias can be a roadblock to new possibilities and we are often too proud to listen to anyone else. I too am a musician and I am just as staunch and set in my ways as any of the other guys. I realize the importance of letting you like what you like and I will NOT try to change your opinion of your current favourite strings (it would't have any effect anyway). This is just some good information that I have found and it may be helpful to you.
Plain strings are usually made out of high carbon steel that are coated in tin to improve feel and tone. Some acoustic plain strings are coated in zinc or bronze for a brighter sound. The wound strings have a core with wire wrapped around it. The wrapping techniques are different for most factories. For Example, DR hand-wraps the strings while other companies use precession machines to do the work.
Get what is most comfortable to use. It is true that a bigger string is louder but, some people say that lighter string equals lighter sound. If there is a tone difference, it I find it to be negligible. For example: ZZ Top guitarist Billy Gibbons, likes a .007 string for his high e, and he has a pretty thick tone. I have also found that when I play metal, a set of 9-42 are just as 'heavy' sounding as a set of 12-56. The heaver ones just make it harder to bend. Thats all.
The Core: Hex or Round?
Until the late 60's, a round core was the only option. Later string companies started using a hexagonal core which made it easier for the wrap to stay on, and delivered a more solid punch with a very quick response. Some companies (like D'addario) use only hex core strings and have had lots of success in creating consistant quality sets of strings. Other companies use both round and hex core strings and report that the round core is more flexible and easier to bend with a fuller sound and more all around versatility. Not better, just different.
80/20 Bronze (80% copper and 20% zinc which is actually brass) has the brightest tone out of the box but can loose this tone quickly. Other "bronze" strings contain copper, zinc and tin and will generally have a sound not quite as bright as 80/20 strings but will last a little longer.
Phosphor Bronze (acoustic)
Strings wrapped with phosphor bronze have a deeper richer sound than the bronze strings. (I love phosphor bronze strings on a good cedar top guitar)
Silk 'n Steel (acoustic)
These strings feature a thread of silk on the inside of the wrap producing a softer tone.
Stainless Steel (electric)
Stainless Steel strings have a very tight, bright and focused sound. They are also extremely rust resistant but they will wear down your frets quickly. They are also recyclable.
Nickel Plated and Nickel (electric)
For rock guitarists nickel plated are usually the way to go. Generally the wrap will be made of iron and then plated in nickel, producing a strong magnetic field which will deliver a high output, with an edge combined with some good overtones. Pure Nickel strings are harder to find. They have a pure nickel wrap around the core and produce a quieter and warmer sound with very rich overtones.
Alloy 52 (electric)
Strings with this alloy of 52% nickel and 48% iron produce a high output, as well as the warm and overtone-rich characteristics of a pure nickel string. These are generally used on vintage style pickups to increase the output while keeping the vintage tone of the pickup.
A coating on a string can greatly improve the longevity of a string. Some coatings are more sonically invisible than others. For example Elixir's nanoweb strings have a coating that is so fine that you cannot feel it under your fingers and personally, I can't hear a difference between these and a set of non-coated strings of the same specs. Elixir's polyweb strings however, have a coating that can be both felt and heard. The sonic difference is not a negative effect, just different. Each string company has a different way of coating their strings. My personal favourites are DR DimeBag strings. I usually don't love signature things of other artists, however I cannot deny the greatness of those strings. These wraps of these strings are coated in a liquid polymer solution prior to wrapping and have become my favourite guitar strings ever. Try em! You'll love em!
Cryogenically treated strings
Many companies offer strings that have been cryogenically treated. That means that they subjected the strings to extremely low temperatures to realign the molecules of the strings in order to increase the longevity. Many players have also reported better sustain, and a greater resistance to corrosion due to this process.
Round, Half and Flat Wound
Sometimes the wrap of a string isn't round. Generally its like this
Round wound - Bright
Half rounds - not as bright but a little smoother
Flat - Mello and smooth like buttah. (great for jazz)
There you go! Thats what I know. What are your favourite strings and why?