guitar wood: Mahogany or Alder?

As a rough example, mahogany could be better for soloing and more mellow tunes, when with alder you might get a little more edge and treble to metal riffs or whatever. But then again, I think mahogany has good lows and sustain. Not sure about alder .
 
It all depends on what you like. Try out guitars made our of both.

Usually different guitars come with certain woods, eg most superstrats are Alder or Basswood. Most Explorers are Mahogany.

Just try em both and see what you like.

Also remember some pickups sound like ass in some woods ;)
 
mahogany is more expensive because it is a protected species, being hard to grow and increasingly rare. even though mahogany is a dense wood, it is soft. it is also a very good tonewood. alder is mainly used on bolt on guitars, but remember that most of the les pauls have maple as neck through body. that means that the pickups are actually mounted on maple, the only mahogany is in the wings. obviously this is not true if you have a gibby with a mahogany neck. in fact, the first solidbody that les paul built, "the log" was a solid piece of maple that he later glued wings onto so that people would take him seriously.