Rather than working on one by one work on everything.If you just work on step X only step X will improve your time on the other steps will probably won't improve much.What I just said well could possibly be false but that's how you should practice.If working on everything at once doesn't work for you ( everyone has their own style of practice) ........... looking at your current average you should improve on your F2L and worry about your LL times when you're struggling to go sub-20? or sub-15 but most of the time, LL speed doesn't affect you much if you're going for sub-20 unless LL takes you more than 10secs to finish.
should I get the ShengShou 2x2 or Wittwo ? The wittwo is a bit expensive for a 2x2 for me but is it worth it If I get it or maybe I could get something cheaper like the SS that could possibly have a decent performance ?
Alright thanks. I'll work on my F2L some more, then move on to PLL. @Your question, I have never used the Wittwo, but the ShengShou works great for me right out of the box.