GPS GNSS Accuracy

Please read this page, before.

Who more accuracy U-blox 6 generation (GPS) or U-blox 8 generation (GNSS)?

Global

Operational

NAVSTAR GPS accuracy - about 2-4* m

Glonass accuracy - 3-6** m

In development Galileo - first services should be launched at the turn of 2014 and 2015. Full completion of the Galileo system is expected by 2019

BeiDou - accuracy 10 m in Asia-Pacific (by 2020 global BeiDou-2 also known as COMPASS)

Regional

Indian Regional Navigation Satellite System - accuracy unknown (for India)

Quasi-Zenith Satellite System - accuracy unknown (for Japan)

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 less than 9 meters.