There are no easy instruments. They all take practice and all will take time to learn. Obviously some are easier then others, but becoming good at any instrument is hard. If you're starting out piano is a good choice. Because: 1) you learn a lot of music theory playing piano, witch will make it easier to learn other instruments. 2) You can play a wide variety of music on a piano 3) it's vary common so it'll be easy to find lessons and sheet music.
But if you want to say go into drums, knowing piano won't help much. It'll still help a bit because it'll teach you music theory, but they are vary different. Where's guatir it will help a lot knowing how to play piano.
I would advise just picking an instrument you think you'd like and trying it out. Just keep in mind that it'll be hard starting out especially if you're self taught. Also don't rush out and buy an instrument, if you do get something cheep. Make sure you like an instrument before you buy it.
Universally, the piano is considered the must easiest because in music theory, it applies to most instruments. Guitar follows a different but similar instruction; but it will be considered as Guitar Theory. So you must first learn how to read nots, where notes go wear on an instrument and have a basic idea of how the instrument is used. I still have not learned how to play an instrument. Not one. So I only use DAW.