ESEA or Faceit? Where should i play to increase my skil

FaceIT premium is better than ESEA. You won't increase your skill just by virtue of playing on any one of those platforms. If you're playing against better players you will be forced to adapt but the goal for you is to continuously try new things and play for yourself. Your teammates irrelevant in pugs/mm type environments. I recommend watching demos of pro players (not live streams), and analyze why they do what they do and don't move on until you can inductively reason everything.