With type 2 diabetes, our body struggles with carbohydrates.
Therefore, it is common to focus on carbs rather than fats. Full fat Greek yoghurt contains less carbs.
However, if you have other medical conditions which require you to limit fats, that also needs to be considered and makes life a tad more challenging.
So, if your choice of yoghurt is based on managing your BG, full fat is best.
(Note, I never suggest we can "control" our BG. There is so much more than food, often which is outside our direct control, which can affect our BG, I think of controlling BG in the same way as I think of controlling a classroom of 4 year olds - we may think we can do it 80% of the time but there will always be that unexpected cheeky one who we could never predict/control.)