Radomus was by far the one I don't remember ever getting upset about. After all, I did beat him on my first try. After that comes Luna, who only took a couple, which I suppose was nice considering I absolutely abhor Bennet with a passion (though I do always say "Bennet, I hate your dumb team but I do feel ya bro"), so I already had enough troubles by the time I got to her. I haven't gotten to Samson yet due to the current tile error in Route 2 that I cannot get past, but I feel like he will be a breeze with my Acrobatics Archeops.
The others I've fought would have to be in this order:
Julia - Protean took care of most of it. It was as challenging as the first gym should be. Getting used to the game and all
Shade - It did take me a few tries, but once I got a structure down with Gourgeist, I was fine. Priority moves are wonderful.
Shelly - I don't remember getting too mad. Also her Volbeat never really did anything. No Tail Glow or nothing.
Florinia - The field effect surprised me at first, but I made proper use of Noibat's Air Cutter (and that was the last time my Noibat was ever useful)
Kiki - Honestly I had a very hard time with her. Hi Jump Kicks never missed, and somehow she could always get off a Meditate on Hitmonlee. I ended up relying on Slurpuff again (same way I beat Solaris, with some help), and finished off the Medicham by switching into Gourgeist twice because I knew it would crash itself to death.
Aya - This took me a while because it was the first one I had to grind for. Actually, I needed to get an entirely new Pokemon for it; I trained my Lunatone that I got in passing under the Grand Staircase. It was through this battle that I formulated my go-to strategy for fights that are too difficult for me (exception in Serra)--Mamoswine uses Mist, Lunatone sets up 3 Cosmic Powers, then sets up as many Charge Beams as is safe and proceeds to sweep. Mamo can EQ since that moon rock has Levitate.
Noel - I do remember getting pissed at him. I don't remember what it was. I think I blocked it from my memory. I just know I hated it.
Serra - Haha, screw her! The only one without a field effect and it's the hardest for me?? Most of my team couldn't handle her type coverage very well to begin with. I could never get that Lunatone going because of Cloyster. I had to power level my Escavalier, which ended up taking care of the rest with great caution. Even though it was fine once my Escavalier was adequate, I still recall it being the one I got the most frustrated with.