Hmm...I'd either be a dragon, fighting or water gym...
Dragon
Dragonite, Gyarados, Flygon, Charizard, Aerodactyl, Kingdra
Obviously this'd have to be an 8th gym because dragons. And I'd do the typical thing of half my team not actually being dragon-type. Much as I like Salamence, I'd only have one pseudo, Dragonite.
Fighting
Blaziken, Poliwrath, Breloom, Hitmontop, Hitmonchan, Hitmonlee
No Guard Machamp just seems a cliché tbh.
Water
Politoed, Poliwrath, Ludicolo, Buizel (because fu Floatzel!), Lanturn, Gyarados
Yup, I'd genuinely have an unevolved pokémon in my team as I dislike Floatzel that much. Although maybe swap it for a Swampert / Empoleon.
And yes, I genuinely wouldn't use any Gen V pokémon. Much as I appreciate them, I have more than enough favourites from Gen I-IV so, meh.