Xemu is by far the least desirable option. Immense hardware requirements and relatively limited compatibility. It’s a miracle it’s functional at all. I would only use it for games that you cannot play through any other means - so the small number of Xbox exclusives that were never ported to other systems and don’t work through backwards compatibility on newer Xbox consoles. Midtown Madness 3 comes to mind. I’m glad I finally got to experience this forgotten game by the Battlefield developers - but it was barely playable at 640x480 on a Ryzen 5 5600. The experience reminded me of very early PS2 emulation and not in a good way.
PCSX2 is usually decent and has made immense strides in recent months, but it usually runs multiplatform games worse than Dolphin, which is the gold standard for console emulation. However, not all ports of games are better on Gamecube. While the console is more powerful than the PS2, the limited amount of storage on the system’s proprietary discs resulted in quite a few compromised ports (edit: and the PS2 has a few hardware tricks up its sleeve that no other system of the time can replicate, particularly in the effects department). Still, it’s usually the best course of action to try Gamecube/Wii emulation first and resort to PS2 emulation only if you’re noticing downgrades. There’s also the little issue with PS2 games that some rely on the controller’s analog face buttons for certain mechanics (e.g. short jumps, long jumps, throttle/brake, certain attacks), which are not present on newer controllers most people are likely to be using. Sometimes this can be rebound reasonably well, e.g. to a modern controller’s triggers, but not always.
All of the above also applies to AetherSX2/NetherSX2 and the Android port of Dolphin, by the way. On mobile devices in particular, the lower hardware requirements of Dolphin are worth keeping in mind - although lower-end devices are likely to struggle with Gamecube and Wii games anyway. This is not an issue on PC anymore; even basic PCs from over a decade ago will run Dolphin flawlessly, whereas PCSX2 can be punishing even on modern CPUs with certain games at higher resolutions. The original PS2 version of Shadow of the Colossus for example is so demanding that it’s actually a better idea to emulating the slightly enhanced PS3 port through RPCS3 instead.