Depends on where you camp and what you want to achieve.
Some campsites insist on breathable groundsheets.
The PVC groundsheet or tarp will keep water out, the breathable groundsheets don't. If the ground is wet before you pitch, water will seep up. There are also two types of breathable - close weave and open weave. The open weave will allow grass the grow through if on extended camping trip, the close weave prevents that, but is not as grass friendly.
I use a Bolon close weave groundsheet, it doesn't really need fastening, but I use clingons at the door area to prevent any slippage.