Hiya Kizzy, the main difference would be the warranty and the fill of the implant.
The premium have a higher fill of silicon in the shell so have less chances to ripple, they are also harder to rupture. The standard are covered for 10years whereas the premium have life time cover, so if your implants were to break you would only need to pay the surgical costs and the replacement implant would be free.
Personally I opted for the premuim as I feel the extra fill/cover gives peace of mind. Hope this helps!