Trumpet

There is the common trumpet you can choose or the cornet which is quite similar to the trumpet, so I'll put the two together. If you want a high playing brass instrument, then trumpet is a good choice and it sounds very nice. A good thing about a trumpet is it is pretty small and light, so handling it is pretty easy.

Trombone

 

The trombone is a great instrument to choose because it's the only brass instrument that I know of that is able to tune itself easily with a slide while playing. A cool thing the trombone can do is a gliss, which is when the trombonist moves their slide forward and backward smoothly, which is used in a few pieces and I think it is used in jazz a bit. Also a trombone with a special trigger can be played up to an average flute note by an experienced trombone player.

Baritone

 

Baritone is the closest thing to trombone in my opinion because the two play at on the same octave but have different ranges. The baritone is slightly lower sounding than the trombone. I played baritone before and was pretty fun so this instrument is pretty cool and its design is similar to the tuba except the tuba has more slides and pipes. A special baritone with two bells (which aren't produced anymore so they're antique) can be played so that a baritone sound comes out of the main bell and a trombone sound comes from the secondary bell which is very interesting.

Tuba

Tuba is what I currently play and you get a lot of props for playing it in a marching band (marching tubas are called sousaphones) because its heavy to march with. The only bad thing about tuba is it is usually large and pretty heavy, making handling it somewhat difficult. In my opinion tuba is probably the easiest instrument for a beginner to play because its mouth piece is large so you can buzz (flapping your lips or vibrating it in the mouthpiece) and make a sound easily, though a nice sound I can't guarantee. So tuba in my opinion is the easiest instrument for starters and is a valuable component to any good band.

French Horn

If your up for a challenge with an instrument then French horn is a good choice. To me the French horn is the most difficult instrument to start with because buzzing in it is a pain because it is as small as a trumpet mouth piece and the way its shaped makes it weird to blow in. If your in a beginning band with French horn you won't usually have to care if you stink or not because French horn is really difficult to play and the music teacher will probably give you a break.

Those are five common instruments of an average band that are brass, so if your choosing a brass instrument to play think about the pros and cons of what I said. Good luck playing!