Since the guitar world is booming and expanding at a fast pace, lots of new stuff is showing up on websites. We can now practice more efficiently than 10 years earlier.

Now, we have access to those websites ; GuitarInfusion.com, GuitarPlayback.com, Yousician, Musicism, JamTrackCentral.com

Can somebody tell me what is the best ? They each cost around 20 $ per month.

Yousician and Musicism seem to be targetted towards beginners.

Guitar Infusion is amazing, but seems to target Improvisation Addicts with extensive theory knowledge.

GuitarPlayback gives you CHOPS, LICKS, and MOVEMENTS to upgrade your musical phrasing, exactly like JamTrackCentral does.

Can somebody tell me if you made significant improvement by using the Interface itself ?

I really can't say I recommend any of those. I think it's a great idea to get a teacher; and I think that it's a great idea to study online on your own. However, I've never liked the idea of an online course/"teacher". I think that they combine the worst sides of both approaches: the lack of personalized input and mentoring in online lessons and the fact that you have to pay for it.

I can't tell you anything about these websites as I've never tried any. Maybe they're great. Maybe they're useless. You really need an another opinion on that.
Quote by Jet Penguin
Theory: Not rules, just tools.

Quote by Hail
*note that by fan i mean that guy who wants his friends to know he knows this totally obscure hip band that only he knows about with 236 views on youtube. lookin' at Kev here
I'd recommend Pebber Brown. he's improved my playing from playing simply bar chords to trying to play some Paul Gilbert songs, in the space of just 2 years. Everyone's different I guess but can't recommend him enough. He's got lots of videos on YouTube for free check them out.