XenoGC + SD2SP2
I only had a XenoGC at first but I kept getting read errors even after replacing the lens (I tried tweaking the pot, etc). Thankfully, I never had a problem booting discs, only playing them for more than 15 minutes, so it was perfect for SD2SP2 since booting up Swiss only takes a few seconds.
Also, I was surprised at how cheap SD2SP2s are.
Same here with the XenoGC + SD2SP2. I did 2 of them, My silver one (my first GameCube) had problems reading burned discs but, after adjusting the voltage on the laser(pots), it's working fine(many YouTube videos on this). After seeing the orange GameCube, I needed to have one. I did the region mod(so I can have English menus but, could switch back), a XenoGC and SD2SP2. All 3 of my GameCubes have the matching GB player.
Going this route I can still play my original discs. I don't see the appeal to replace the disc drive with a SD card. The option that I am using give me the best of both worlds... maybe not as fast... oh well...