Hi Mel,
I think the best L&P is the one you have the least problems with.
There are lots of different products going from one end of the spectrum to the other - as Carole says - which product have you trained with or are you not trained yet and looking to train?
The first place to start would be to look at the industry magazines - Scratch and Professional NAILS.
Do your research - find out who trains locally to you - even for the best product in the World, if you cannot physically get to the training course then it doesnt matter if it is the best product - hope that makes sense.
Look at products and company's that offer a complete package - training, products, back up service etc.
We all have our favourites but what works for some might not work for others.
Be true to yourself and find a complete package that works for you.