“Not too trendy. We are looking for a timeless look”

This precludes glass, whether sheet glass or tile.

Am I correct in supposing that you are at the early planning stages of your kitchen? If so, it is a bit early to make any real choice. Here’s some basic backsplash advice that you can keep in mind while choosing your other finishes.

To the age old question, "Do I need a backsplash?" the short answer is yes. You need some sort of backsplash in wet zones to protect your walls, cabinets floors and subfloors from deterioration due to water infiltration, and in your cooking zone to protect your drywall from cooking oils, spills, odors, and cleaning chemicals.

That said, plenty of houzzers have chosen not to have a backsplash, or to delay the choice for budgetary or other reasons. Search for threads with ABB (all but backsplash) in the titles to check those out.

How does one choose a backsplash?

First, like every other process here, we encourage you to do some research on your own, then post your particulars and ask for feedback.

One fundamental question you must consider before all others is whether your counter material or your backsplash will be the focus of your space. Consider images of kitchens with busy counters, and those with commanding backsplashes, and decide which you prefer. Bold counters and tile rarely work well together.

To Wait or Not To Wait

Buying your bs material when you buy your other finishes might prevent delays down the road and could help with electrical outlet placement. Drawbacks include that you are making decisions on colors and finishes based on samples, sample cabinet fishes, sample counter swatches, etc... and that samples don't always represent the final product accurately.

Waiting to buy your bs materials until you have had your counters installed allows you to see sample tiles in your space in your light throughout the day with your actual installed materials. If your cabinets are warmer than you expected, or your counter cooler, you are free to search for a bs material that can pull things together. The only drawback to waiting is that you may have to wait for tiles to be fabricated or to arrive, causing possible delays in the completion of your space.

The majority wisdom on this site favors waiting if that is possible. Regardless of which approach you choose, you should consider your bs as one part of a whole picture of your beautiful new space.

Inspiration Images

These really help you to focus on what your kitchen as a whole will look like. They also give the folks responding to your queries an idea of what looks you like, so they won't recommend white subway tiles if all your inspiration images feature handpainted Mexican tile.

Google images of kitchens with your other materials (white cabinets, walnut floors, etc...) and select which ones you like the look of. What type of bs do they use? The idea is not to copy the look, but to get a feel for looks you like, and communicate those looks to others.

Budget

Finally, we'll need an idea of a materials budget. Installation can account for half of the budget for a backsplash, so take that into consideration in your planning, and deduct accordingly, and let us know how much you want to spend in $/sf for your materials?

It's not very helpful falling in love with a handmade tile in a custom glaze if it costs $100/square foot and your budget for tile is $10/sf, but houzz members are fantastic at finding similar (and occasionally the same) tiles for less money. Without budget numbers it is very difficult for us to truly be of help to you.

How we can help.

The way it works is that we can recommend a surface (usually tile, sheet glass, metal, slab stone or laminate), advise against a choice (color, or busy-ness are the usual reasons), provide you with layout and pattern feedback, and images you might have missed of materials that have worked for us or caught our eye.

"How can I find a bs tile to go with my green floors, counters, and purple cabinets"

The answer might be that you have to paint your cabinets or change your floors to make it right, or maybe some houzzer somewhere will show you an image of a kitchen with a painted tin backsplash that pulls it all together. It has happened before.

Some houzz members are great at photoshopping images together to give you an idea of what a small sample of tile might look like in your space. It is time and effort on their part that can be truly helpful. Remember to say thanks.