It really depends on what you want to prioritize:
- Budget: Get an RT2X, and go YPbPr or S-Video for the PS2, and S-Video for everything else.
- Pros: Cheapest option to play your consoles, low lag, S-Video good enough value to some, S-Video cables generally cheaper than SCART
- Cons: No accommodation for 31kHz+ (480p+), no good deinterlacing, no RGB
- Lagless line multiplication, RGB, picture quality, and/or lagless line multiplication: Get an OSSC and an RT2X; go RGB for SNES, PS2, and GameCube, and S-Video for N64.
- Pros: Low lag, RGB support, 31kHz+ support, line multiplication up to 5x for 240p/288p sources
- Cons: No good deinterlacing, still costs Framemeister money, more video processors means more cable mess if you’re not mindful during setup
- Deinterlacing, picture quality: Get a Framemeister; go RGB for SNES, PS2, and GameCube, and S-Video for N64.
- Pros: RGB support, 31kHz+ support, extensive scaling options, good deinterlacing
- Cons: Expensive, adds about 1 frame of lag
I understand not wanting to modify your consoles, but, in some cases, getting an RGB or HDMI modification installed is going to get you the best experience. The N64, in particular, shipped without any RGB support, which means S-Video is going to be the best an unmodified example can muster, even though it uses RGB internally. If you get your N64 fitted with an UltraHDMI, you can skip the RT2X, OSSC, and/or Framemeister and connect it directly to any HDMI TV; it will scale all output to your choice of 480p, 576p, 720p, or 1080p at your choice of 50Hz or 60Hz; and it does not suffer any of the HDMI resync blackouts that you’ll see with the other devices when the console changes video modes (RE2 is arguably unplayable due to using 240p for gameplay and 480i for menus).
The SNES (and NES, for that matter) suffers from an inconsistent sync cadence that a good amount of modern hardware doesn’t tolerate, so a dejitter mod may be necessary for compatibility (and a combo dejitter+RGB bypass board pairs well with the SNES mini/Jr, which had S-Video and RGB removed).