The guitar is definitely a lot easier to figure out and after a while you'll definitely see improvements. The guitar is also cheaper so if you just wanted to try it out that would be better. But the piano is definitely in the long run, the better instrument. No offence to guitar players but the piano generally sounds better than any other instrument. But it will take a lot longer to learn.
The pros of a guitar is that its cheap and easy to learn. You'll be able to sound good after a while. The con is that you'll never have that "full" sound that piano music has. If you can sing guitar will probably be a lot more fun for you.
The pros for piano is that you will be able to play amazing and beautiful music. You will also be able to play well known music that will impress people. The con is that it takes a lot of time and money.
I'd say that if you're already in highschool or further play guitar. You'll only get frustrated with the amount of time it takes to be good at the piano.
Also if your considering taking a new instrument and you want to play classical music but you you're still flip flopping with the idea of playing the guitar. Why not check out the violin. There's a lot of beautiful classical music plus if you've got a good ear you can easily play some of your favourite tunes no problem. I just bought a new violin. Cheapest is around 350 and the most expensive can be in the millions.
My dad's family is very musical, so there were always instruments lying around the house when I was a kid. The second we showed interest in any instrument, my dad jumped at the chance to teach us to play it. When I was 5 or 6, he started teaching us piano and by the time I was 12 we were learning guitar. To be honest, I find that knowledge in each instrument helps me to play the other better! Just a tip though - when the tips of your fingers hurt from playing the guitar, don't give up; it does get a lot easier...
OMG guitar! What an amazing way to spend your time. I currently own 5 guitars. I love to play and I do so every single day. I have been playing for 2 years but have come a long way. The best thing about guitar, I think, is that you don't have to take a single lesson to be good. My grandpa has been playing for 50 years and he is SKILLED. My dad played for 20 years and he was SKILLED. I've been playing for 2 years and... Well, I'm getting there. The one thing we all have in common is that we've never had a lesson in our lives. Ever. You can just improvise, just sit there for a few minutes every day, and you can teach yourself. You don't need some teacher to show you how to play each individual chord, to define each individual note or fret. You can just pick up a guitar and play. You can just plug that baby in and strum. Place your fingers wherever they'll fit and go along with it. Listen to your favorite song on repeat 5 times, pick up the bass line and plink it out on your guitar. It's such an amazing accomplishment, to figure out a song, even to figure out a chord. You think, "Wow. I just played that. Me. I did. I just played a guitar and it sounded good." How amazing it feels to tell yourself that. I honestly think you should learn to play the guitar. It's a really great opprotunity that you should take while it's still there! Happy playing!
Between the two, unless you would like to become a professional musician, I would pick up the guitar. For starters, the guitar is much cheaper to own. The cost of guitar ownership is minimal, as the price of a guitar is generally less than even an electronic keyboard. The guitar would probably be more difficult to learn, but the ease of ownership and ability to take it with you should help overcome the learning curve.
Both are great instruments, but guitar is easier and much more versatile. You can learn the basic chords which are the foundation of most songs in just a few minutes. Guitars are much more portable, so you can take a guitar with you when you travel, and singing while you play guitar is also much easier than piano.