Baritone/ Euphonium

First of all let's clear up the difference between the two instruments. The Baritone is in the key of B-flat, is placed an octave below trumpet and has a conical shape. The Euphonium shows all of these traits as well though. The difference is the valves. Euphonium has four valves and the Baritone has three. Now that that is cleared up lets talk about the genres. Typically all instruments are important somewhere in music. Like an oboe in classical or a saxophone in jazz, but the Euphonium and the Baritone serve no real purpose to me. At the high range of these instruments they can sound very beautiful. But then again the french horn can play the same notes on the same octave and be able to control the sound better. It even has the same mellow sound. The middle stuff can easily be played by a trombone player and the low stuff can be covered by a tuba player. These two instruments could be taken out of every genre of music except one. Some drum and bugle corps don't let the slide trombone into their bands. In this case they call in the baritones and depending on how low the part goes the euphoniums.

Tuba

I play a little tuba and although I'm better than anyone in my school, I am no where near professional level. The tuba is one of the simplest instruments to pick up an learn the basics. But a real tuba player has to practice constantly to stay good and to get better. Tuba belongs in the classical genre of music mostly although not always used. Many orchestras don't have tuba players. Marching bands is where the tuba player can shine though. Give them a contra bugle or a sousaphone and they can go places. But a real tuba player plays in classical events. I've even heard a tuba play Carnival of Venice.