Go for the Defender's Greatsword, and infuse it with lightning. Very few enemies are resistant to lightning in PvE, making it all the more effective. Plus, the in-built buff will save you from having to attune Sunlight Blade. I believe it has a higher AR than the Thorned Greatsword too as long as you have high Faith. The Thorned Greatsword isn't bad, but the fact that the heavy attack makes the weapon do the special attack makes it a lot less viable for PvE in my opinion, especially with the durability bug in SotFS (and vanilla DkS2 on PC).