which do you prefer? piano or guitar...?

Hmmm, both are typically string instruments... well, unless the piano is like those that you need batteries if not an outlet in which you have to plug it into. What to choose, what to choose...? In case you can have both, why not? But seeming that you did mention that you have been thinking alot between the two, I guess you have to consider if you move around like a performing musician. You can move around with your guitar unlike the piano.. That's just one thing among many that we can think of in deciding on which item we like to get if we are to choose among selections.

It depends upon what you prepared most or what instrument you can play the best. you cannot play such instrument one at a time and so you will have to stick to learn to play professionally. Find your instinct, think about what you love most and you will be guided accordingly. Happy mylotting!!