I've played guitar and bass for a long time, and I play a little piano. Like you, I took piano lessons when I was a little kid then quit. Then I picked up the guitar when I was around 12 years old.
In my opinion, both instruments are as difficult as you want them to be. You can learn some basics and get by on either, or you can immerse yourself in study and become an expert on either.
I think there are way more resources for people starting out on guitar, particularly the use of tablature for learning songs. To learn songs on piano you usually have to known how to read music. So in that sense maybe guitar is a little easier. but be aware that music theory is the same for both. The relationships of the notes on the piano are simpler to visualize because the they are all in a line, but once you understand how the guitar's tuning works you'll see a direct connection between the piano keyboard and the guitar fretboard.
If you want to learn guitar my advice would be to learn to tune the thing, pick some easy songs you like, look up the tab online and start trying to learn them. This will get you started learning some basic chords without getting bored. At the same time, research left and right hand technique, scales, music theory, etc, and you'll begin to understand how it all applies to the guitar. Before you know it things will click well enough! :-)