GPS GNSS Accuracy

Please read this page, before.

What is more accuracy U-blox 6 generation (GPS) or U-blox 8 generation (GNSS).

First of all where are you from? If you are from Russian or neighbors country than yours better choice will be U-blox 8 generation (GNSS) if not choose U-blox 6 generation (GPS).

Why so. According to this document, accuracy of GLONASS outside of Russia is more than 10 m.