That's a great question

Really depends on the situation:

For example one factor would be if your enemy uses auto-barrier and is faster than you, then you would rather use Normal Gaara.

2nd important factor, if you are using it in GNW/Bond then you would rather want Kazekage Gaara because normal Gaara barrier buffs only your team and not your teammates.

Overall I would say:

Normal Gaara better if you are weaker/slower, Kazekage if you are using some damage/nuke teams and confident with having the auto-barrier.