I thought I would post a follow up for anyone else that may be in my position.
I have a SNES, N64, and Gamecube all connected to a single LCD TV. My desire is to use SVideo for all systems. Currently, I am using a combo SVIDEO/Composite multi AV cable for all the systems. I am manually unplugging and plugging it in to which ever console I want to play.
The cable I am using, while having both the composite and SVideo cable is decent. This cable does not cause Checkerboarding on the SNES but with the N64 it does. I recently bought the Gam3Gear Svideo cables from Amazon
https://www.amazon.com/gp/product/B00LE3EAIK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1. These cables only have the SVideo connection. These are worse than my combo cable. I tested both cables for continuity with my multi meter. The combo one I have has both ground pins connected while the Gam3Gear only has the one ground pin. The Gam3Gear cable DOES NOT have the composite pin connected at all. Both have the correct Luma and Chroma pins connected for proper SVideo. There are a lot of people claiming that some cables route the SVideo over the Composite pin. This Gam3Gear cable causes Checkerboarding on the SNES and even worse on the N64, while not even having the composite pin connected. Again, the combo cable I have has better results on the SNES and a little less Checkerboard effect on the N64 in comparison.
I have hooked both cables up directly to a TV's SVideo connection and through a HDMI to AV upconverter. Both give me similar results as far as Checkerboarding.
So what does this all mean? My guess is just too thin gauge of wire being used and/or poor shielding.
I also purchased the Radio Shack 4in1 Component,SVideo,Composite system selector with a remote
https://www.amazon.com/gp/product/B006PIPOBQ/ref=oh_aui_detailpage_o00_s02?ie=UTF8&psc=1. This is a powered device. When using it, both cables give me the Checkerboard in an even worse way. So either this device is causing even more signal loss or there is something else going on.
So now I am back to square one.
I am now on the hunt for quality SVideo cables and system selector. As the ones I bought are going back. I found an eBay listing from a dude in Sweden who hand makes them. I thought what the hell and it should be on its way. Here's the link.
http://www.ebay.com/itm/NINTENDO-64-S-VIDEO-HIGH-PERFORMANCE-FULLY-SHIELDED-GROUNDED-PAL-SVIDEO-N64-NEW/172587717894
As far as System Selectors go. I am reading positive things on the Pelican 4in1 or what looks like a rebranded version of the Pelican one from Gamestop. Both of which are unpowered.
Looking for advice, if anyone has any recommendations on which switcher and SVideo cables to buy. Thanks!