For a kitchen backsplash that extends behind a cooktop, big glossy tiles with minimal grout line width, like 1/8", makes cleaning a lot easier. Behind a cooktop, even with a good vent hood overhead that vents directly to outside, stuff is still going to spit and grease condense on the surface. Grout is a lot harder to clean than a glossy surface. Narrow grout lines means using unsanded grout, which I find is trickier on estimating setup time till wipe than sanded grout.
A few years ago it was the rage around here to make kitchen backsplashes out of little rectangles or other cut shapes of... can ya believe it... Travertine! Travertine, with all its natural holes and pockets, behind a cooktop! DW and I wondered how much ground beef those pockets would collect. Plus with small tile bits, all the grout lines, the total surface area in grout per square foot! On the other hand, a wall with small dull pocketed tiles like Travertine probably won't show a poor tile installation job (lippage, in-out-in-out like noisy road pavement, etc.) like glossy tiles will.
A good glossy tile job will look nice, and forever be easy to clean.
It's inevitable when laying tile that you will get some mortar sticking up too far between some tiles here and there. I have small pieces of thin cardboard, like 3" long by 1/2" wide, cut to size and pre-folded into a U around an object about the grout line width. For 1/4" wide grout line, a pencil works good. Narrower, a solid wire or whatever. I use them as a scoop, then throw out each one. Its quick and doesn't smear the the tiles with the mortar as it removes it.
Back Buttering - I ALWAYS back-butter tiles as the last step before placing a tile. When buttering, I really "burn it in", a thin layer all over the whole tile with the non-notched edge of a trowel. I have the tile laying upside-down when I do this, not holding it in the air by hand. So I can really burn it in to get maximum adhesion of the mortar to tile.
Grouting - The bigger the tile, the less grout cleanup you should have to do. I have never smeared grout all over bigger tiles with the float. Just near the edges of the tiles.
Oh one last thing - SAFETY! - Wear safety goggles when cutting tiles. I don't care if some tile setters that didn't graduate high school don't wear them. Even hands can get nailed pretty good with little sharp shards of porcelain tile when cutting with a diamond wet tile saw. I have a sprinkling can nearby to wash the tiny shards off my hands and the just-cut tile. And yes, I always cut tile outside.