Layout low noise LDO

[noisepic]

I have low noise LDO supplied by a buck converter, these on top layer and layer 2 is GND plane only. I CONSIDER 2 way of Gnd design:
1. Seprate their gnd on top, having via to layer gnd2
2. Share the gnd, both gnd having via to GND at layer 2

Which case is better ?

[robertferanec]

Normally I just use one common GND plane. But ... I normally design digital CPU boards, it may not apply to your application.