The main fights in raid roulette that trip people up seem to be A9 (the Refurbisher, because people try to ignore the generators) and O11 (Omega, because the Starboard/Larboard mechanic still gets people). Sometimes E5 (Eden Ramuh, just because there's a lot going on) and P3 (not-Phoenix, because it's just a visually badly-designed fight, all the colors blend together and make it hard to see what's happening).