In advance: Sorry if this is wrong forum or whether im not supposed to ask (I searched and looked at FAQ)

Basically what gauge strings do I need? I have a http://www.ultimate-guitar.com/reviews/electric_guitars/yamaha/erg-121/ Does the gauge affect the sound? If yes im looking for a country/blues sound.

Also what string do people prefer? I was looking at earnie ball but I really don't have any idea

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I believe Ernie Balls are the best. Because they cover such a wide range for anything.

Since you want a country blues sound, I would recommend gauge .10 (regular slinkys)
ESP LTD Viper-50
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Zoom 505 II
For country and Blues you would be best of with either .9 or .10 for the bends and what not.

In my past experience i found that Ernie Ball strings lost their newness quite fast (But alot of strings do) but overall they are good strings.
String gauge has an effect on sound, but in your case, I really wouldn't worry about it. Regardless of musical style, I always recommend that beginners start with very light string gauges like 8-38 or 9-42. It makes fingering notes easier, and makes techniques like bending and vibrato easier to control. And it will help you gradually build finger strength and your callouses.

As you become more experienced and develop technique and finger strength, you can move up to a heavier gauge string if you wish to do so. But generally, most country and blues guitarists that I know tend to stick to lighter strings gauges because it will give more of that 'twang' sound associated with country electric guitar than heavier strings that give a more powerful sound.

As for string longevity, different brands work differently with different people since each company treats their strings differently. Everybody's sweat is different with different acidity levels. Some people rust out certain brands of strings faster than others. You can't really take someone else's recommendation there. That's something you have to figure out for yourself.
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