I had the same thoughts before reading everyone else's posts...The 3 x 6 is more 'standard' and traditional, while the 4x8 would be a little more unique and bring a modern or industrial twist or zing to your kitchen...which I can like with traditional elements. Depends on what you want it to do. And Plllog does have a point about smaller tiles fitting in around things better, but I wouldn't necessarily let that decide it for me. Will one fit in the spaces using whole tiles, while the other will require cutting all the way along? (Remember to figure in grout lines) Even if I liked one better, if the other fit in whole, THAT could sway me to change my mind.

For practical reasons, I don't like marmo click in the kitchen, the reason being that the layer of lino on top of the cork base is very thin, and I've had some gouges/dents. Now that I think about it, the gouges didn't penetrate to the cork, but it just seemed like the cork was too soft for a kitchen application. One of my friends also had click in her kitchen and said she wouldn't do it again, for the same reasons I mentioned. So, I would recommend one of the options that includes the sheet marmoleum. I like it paired with the funky yellow and white BS. I also like the idea of a plain yellow backsplash--it creates a nice chunky colour -- I think the term is 'colour blocking'. Slightly warmer than than the straight white BS. Really, I like all your options :-) but I highly recommend marmo sheet rather than click. You can do 2 graphic elements as long as they are completely different in scale (this is what I read somewhere). Marmoleum feels and looks wonderful!

Don't rush the decision because the contractor is ready to tile!!! The backsplash can wait until you find exactly what you want. People on this site have waited up to a year or maybe even longer to do the B/S. If you're not sure and want to wait, maybe you can get a credit from your contractor and have an independent tile installer recommended from where you buy the tile do it down the road. If we hadn't decided to do a full-height granite B/S, I would have waited to see how everything came together and then taken my time to shop...there were too many other decisions that have to be made that you CAN'T wait on...the B/S you can!

Someone else just posted a completed remodel with that same last tile I think. It looks really cool if you have a big enough wall space for it! https://www.houzz.com/discussions/6201378/the-remodel-that-took-a-year