I have bought an DBZ electric guitar, I would like change the original strings, what would you recommend for Symphony X style?
There isn't a best string for metal. You might want to pick a different alloy to make your guitar sound brighter or warmer. This won't be significant for metal, though, because you won't be able to tell when you're playing heavy distortion. You'll also want to consider string gauge. The string gauge is up to you and just depends on what you're comfortable with.