What is the best service to use for learning? I'm looking into TreeHouse right now.

There's also Sololearn. However it only covers the basics. It's great at explaining, but the community sucks.

Just do some free courses on all plattforms. Like Udemy, Udacity and so on. Then decide for yourself!

Call me old school but I recommend buying plain old books (or their e variant if that is your thing). Personally I find the online courses to only cover the basics and leave out details. But hey if you just want to learn to write some code they are probably great!