Imo they are all equal if you talk about normal gathering. With Hardsilver Ore grid in Drav Hinterlands i get like 500-600 wind/hour, any other 51+ grid will net you the same. The best method for crystals is farming Ephemerals: http://ffxiv.consolegameswiki.com/wiki/Ephemeral_Nodes
If I get it right Ephemerals will be possible with Miqo’s scenarios. For now I farm them manually, around 1,000 Winds and 1,500 Earths per hour. If you dont need earth you can just afk for 40 minutes while winds respawn. Rotation is SM+DE, IA, SM/DE (depending on proc), MA. Aim for purity 2 because p3 and higher may result in Duskborne which is cheap. And ignore common Lv56 collectables they are a waste of GP. If you don’t see a Lv58 Hidden or Lv60 Hidden close the node and respawn.