Asking a question like what is the best acrylic, will not really get you a definitive answer.
We are all going to tell you that the one WE use is the best
!
There are a lot of premium brands out there, CND, EzFlow, and Harmony are 3 I have used and have found them all excellent for ease of application and longevity. EzFlow took a bit of getting used to as it is a different mix ratio liquid to powder from CND I was used to, so I would always advise doing a Conversion Course before switching systems.
NSI is not a system I have ever got to grips with, I don't know why but I tried it and just didn't like it, but I know lots of geeks get great results from it. Maybe if you start with it it is fine, but having used CND first I definitely felt I was downgrading when I tried NSI....sorry just my personal opinion.
So although we may not all agree on what is the best acrylic (L&P)!system we do all agree that
you should not mix systems !
Use the full system for whatever brand you choose for optimum results...and your Insurance cover
and buying Professional products from Fleabay is a definite no no too.