Reasons guitar is good...

10. Guitar is portable. You can take that guitar anywhere in the world. Just sling it on your back and go! The music goes with you everywhere. This is a big strike against the piano, organ and drums.

9. Guitar is Heteroponic. That doesn't mean that boy guitar's are attracted to girl guitars, it means that it plays more than one note at a time. Actually, the guitar is also capable of homophic and polyphonic music as well. Keyboard instruments also have this quality but guitar is still better (see point #1)

8. Guitar is capable of flexible tuning. You can tune a guitar's strings to alternate scales or bend notes to create micro-tones. Unless you have a bend wheel on your piano, good luck with this one.

7. Guitar is the most universal instrument across cultures and genres. Guitar or something like it (plucked strings, a reverberating body, and a neck with or without frets) can be found in almost every culture of the world. Guitar can be heard in heavy metal music, classical, jazz, R&B, bluegrass, you name it.

6. Guitar is a social instrument and yet a solitary instrument. You can play all by yourself or you can play in any size ensemble (especially if you have a big enough amp).

5. Guitar has the most number of toys to upgrade it. There are hundreds of different effects, cables, picks, straps, amps, cases, pedal boards, processors, and other bells and whistles that can be added to your rig.

4. Guitar is the most bang for your buck. It is possible to buy guitars that are more expensive than your house, but they are fundimentally the exact same instrument that you can go out to Wal-ly World and buy for less than $100.

3. Guitar is the instrument with the widest range of timbers. That means it has the most variety of quality's of sound that can be produced. Guitar can be soft and tender or loud and harsh. It can create sensative vibrato like a wind instrument or can be thumped and slapped like a percussion instrument.

2. Guitar is the easiest instrument to learn. You can literally be playing chords on the guitar in a matter of hours.

and the number 1 reason why guitar is the best instrument in the world...

Chicks dig it.
http://worshipinthecity.stlouisblogs.org/archives/2005/08/top-ten-reasons-why-the-guitar-is-the-best-instrument-in-the-world.html