Here's how I rank them in difficulty for the latest playthrough. I had a certain team with glaring Fire, Electric, and Flying weaknesses in my latest run. Keep that in mind.
1. Tate and Liza. I HATED fighting these two. Calm Mind + Psychic caused a lot of problems. The Elite Four were easier than these guys.
2. Brawly. Only thing saving me there were my trusty Bug-types, who became liabilities as soon as Wattson, Flannery, and Winona came around.
3. Wattson. Magneton gave me a lot of trouble since I didn't have anything to really damage it. But, Shedinja came through for me. But like all non-Grovyle pokemon, I eventually boxed it.
4. Norman. He wasn't actually as difficult on this particular run than he was on others, even when I picked Torchic. This is thanks to my trusty Swellow. 8 HP. Linoone had reduced it to 8 HP. But, Endeavor saved me. One Quick Attack from Grovyle and Slaking was down for the count.
5. Flannery. Not as difficult as you might expect. But, at that time, I had ditched Ninjask and Dustox, adding Koffing and Wobbuffet to my team. Wobbuffet was the key here. Torkoal pretty much killed itself.
Also 5. Winona. By the time I fought Winona, I had edited my team even further. Only two members of my original team, Grovyle and Swellow, remained. Swellow and Wobbuffet once again proved their worth. Not the first time they helped me. Skarmory and Altaria became much easier because of those two.
6. Juan. Sceptile and Walrein made quick work of him.
7. Roxanne. I like Roxanne, but does ANYONE (who doesn't pick Torchic) have trouble with her?
And there is my synopsis of my gym battles.