Super saiyan god's power  is a bit more  complicated . there's a huge debate going on saying ssj god is stronger than ssj blue and for the people who says that your dumb as shi..... I mean your wrong. Ssj god just has more advantages such as the following

1. Healing
2. Requires way less energy infact it requires almost no energy at all because the energy ssj god uses is inner energy meaning the energy within  more than physical energy
3 and is very useful in speed
But take a look at ssj blue advantages in the following

1. Speed was already proven in the frezza saga in dragon ball super

2 the power ssj blue uses is both inner and physical energy making strength 10x stronger for ssj blue
3.ssj blue gives more technique and power for blue

And there is much more for blue that nun of us even know about but with the combination of inner and physically energy makes it harder to keep stamina however since goku and vegeta have been training ever since they learn that form they know how to master and maintain that form at a good level