This is not a straightforward issue.
I always used a PVC groundsheet, but a couple of sites I wanted to use require breathables, so I picked one up cheap on ebay (as always)
FOR breathables;
Much nicer underfoot,
Less damaging to grass,
Bbetter looking,
Water drains away through it
AGAINST breathables
More expensive,
More difficult to clean when muddy,
Heavier,
Bulkier
More expensive,
In heavy rain, I have had water come UP THROUGH the sheet!
To some extent it depends what your awning is for. Ours is the lounge of the unit, so a good groundsheet is desirable, though we have operated without. The breathable feels more like a carpet, but the experience of water rising up through it was most disconcerting, and unsatisfactory.
I'm still not certain where I stand! (As long as it's not in a puddle).