THese are all challenge sites, to improve skills.... Not sure which ones are the best/most practical... A lot of sites have useless exercises, where you're not learning anything practical..... if that makes sense.


https://www.codewars.com/
https://www.codingame.com/start
https://www.hackerrank.com/
https://codesignal.com/
https://codecombat.com/
https://www.topcoder.com/
https://projecteuler.net/




Would really appreciate some insight if anyone has any experience with any of these sites....

Those sites' purpose lies in algorithms, logical thinking and puzzles.
If you are about to learn practical things, you should create your own project and realize it step by step.

Nonetheless, I liked codewars. Projecteuler is nice, too, but it involves kinda lot of mathematics, so be prepared for it.
I may recommend spoj, also: https://www.spoj.com/