Garb/Drampa will be the best by far. Volcanian will more than likely be traded out for the Ho-oh GX decks. And Gardevoir GX will be tier 1 just because of its match-ups against everything not named Metagross GX.
...make that "Volcanion" "Turtonator" until September 2018(when the format will likely shift to SUM-On), as Ho-Oh-GX is a Basic Fire w/ a different weakness than Fire's normal weakness to Water: Electric, in a similar vein to Yveltal-EX back in the day, only that unlike Yveltal, Ho-Oh can take advantage of Volc's Steam Up, and w/ 2 Steam Ups, you only need a Fighting Fury Belt attached to make its Phoenix Burn attack deal 250 damage--enough to KO any card printed outside of Wailord-EX w/ attached Fighting Fury Belt(290 HP w/o tool removal) and Crystal Wall-holding Black Kyurem-EX(300 HP w/ said Wall attached, again w/o tool removal)--but since you can remove their tools w/ Field Blowers, no problem there outside of the necessary two Steam Ups and Belt, not to mention that they removed Fire resistances after the RSE TCG sets, which are not legal in Expanded outside of select reprints for Trainers, basic Energies, and select special energy cards, so you don't need to go Choice Band to go for the damage you would need to KO everything printed had Resistance been a concern nowadays--since there isn't a card in Expanded, or even Standard, that is resistant to Fire...
^ Thus, Turt had its time in the sun, and now I believe it's Ho-Oh's turn to take its place in the spotlight... and when Steam Siege rotates, Turt will resurface in Volc's place for Shell Trapping purposes in Standard, but again, I believe Turt will see less play in Expanded in favor of Ho-Oh and its unique weakness, and most of all, Phoenix Burn for 180 base(before any additions, including those from Steam Up and/or tools)...