I'm honestly starting to prefer Turtonator over Ho-oh right now. Sure, Ho-oh has a stronger burst with its second move and has fewer conditions for knocking out the bulkier Pokemon in the meta, but Turtonator has much stronger mid-range options. Turtonator can attach Energy to its allies freely for 1 Energy, and his 2nd move is easier to use repeatedly while staying out of range of Gardevoir-GX's attacks. Even if your short on Energy, Shell Trap is a fantastic move on its own with Volcanion-EX as an ally. With Volcanion-EX around, you should be able to average 50 - 110 damage per attack plus an additional 80 if you're opponent doesn't have Pokemon Ranger or Guzma.
Personally, if I had to use both, I would want to include more copies of Turtonator-GX due to it having more flexibility, but if I was expecting more Ninetales-GX or Gardevoir-GX, I would use Ho-oh-GX for the extra burst damage and lack of a Water weakness.