Mozart or Beethoven?

i would perzonally erfer beethovan over mozzarty, but liasten to liszt

play some and see waht grabs you! Dooesn't matter which composer you listen to first

Mozart is my favorite. 

You begin to listen to classical music making your own choice. There is no first to get into. You listen to whichever composer you chose to. Perhaps you should begin by listening to classical radio if there's a classical station in your city. Also cable  have classical music channels where you can listen to various composers and began learning to appreciate that genre.

TCHAIKOVSKY AND WAGNER BEBE

It doesn't have to be Mozart or Beethoven, nor are there any composers you "should listen to first."

I discovered I enjoyed classical music when I was 5 or 6 years' old, (I'm 75) and the first composer's music I remember was Mahler - his 5th Symphony. For me, that was a very good start, because I wanted to explore the rest of his music. After that, I tried Sibelius and Wagner; to this day, I love them still - their music, that is☺

I like Mozart and Beethoven, although I often find Mozart's music a little too 'simplistic'; Beethoven's music has, in my opinion, greater depth and complexity, which makes it all the more enjoyable.

But, hum ho, that's only my point of view.

Beethoven!.....

Both. You should definitely do both. Start with Mozart and once you're getting accustomed to his work bring in some Beethoven.

For Mozart I recommend Violin Concertos 4 and 5, Clarinet Concerto in A, Symphonies 25, 40, and 41, and Eine Kleine Nachtmusik, which plays like a Symphony (basically a work in four movements and involving the full orchestra) even though it wasn't classified as one. Mozart's Requiem is also worth checking out, though I should warn you that the entire work is about one hour long.

If you can make through Mozart's Requiem, you are ready for Beethoven, whose works tend to much longer than Mozart's. I recommend Piano Concertos 4 and 5, Violin Concerto in D, Moonlight Sonata, and all the Symphonies (except 2). You'll notice that Beethoven's 1st Symphony is similar to Mozart both in style and length (being shorter compared to his later symphonies). By contrast the 3rd Symphony and all of his symphonies thereafter are much longer and distinctly Beethoven in style. The 3rd Symphony is considered by many music academics to be the transition from Classical to Romantic.

Then you'll have to explore some of the Romantic/Nationalist composers like Tchaikovsky, Prokofiev, Saint-Saens, Dworak, and Orff.

By the way, when you listen to a symphony, treat it like an album and listen to it all the way through. You're not going to love everything, but if you skip ahead you might miss some wonderful stuff. So at least the first time you listen, play it all the way through.

EDIT: Bringing it back to the 3rd Symphony, the Second Movement (youtu.be/arfHsnxE-MU) is a great example of what I said in the previous paragraph. The first half of it is slow and melancholic. A person unfamiliar would likely get bored and skip ahead to the next movement. But you if keep listening to it, you'll find that something interesting starts to happen around the 8:45 minute mark. The music begins to crescendo. And then at about the 10:30 mark it hits you like a freight train. By the 11:00 minute mark we're back to slow and melancholic, except that the second half of the movement seems change a lot in mood (almost as if going through the 5 Kubler Ross Stages of Grief). That 8:45 to 11:00 minutes perhaps one of my favorite passages of music, and I would have completely missed it.

Beethoven wrote a fairly small number of pieces late in life that move me as deeply as any music ever made. Mozart seemed to effortlessly churn out an endless stream of flawless masterpieces starting from a young age, none of which comes close to moving me as much as Beethoven's best work. Personally I'd recommend starting with Beethoven.

Start with Mozart but I find his work somewhat repetitive. It gets old fast. Beethoven is never repetitive.