I don't know that I'd use marble OR travertine in a shower to be used by kids. That's just a little TOO much masochism for me!! LOL As for a master shower that will only be used by the homeowners, that's a different story. If I had to look for ANY advantage of one over the other, it would be that travertine has holes that are filled, while marble doesn't, and while that shouldn't be an issue, it is, because of unscrupulous manufacturers, flooding the market with cheap travertine. Bottom line-- if you find a good quality travertine, there's on advantage of one over the other.

The very first thing you do is verify deflection and how it relates to chosen tile material's rating. You must look at the whole thing from structure> Joist> underlayment> subfloor before even talking about cement board and crack isolation. You are asking such novice questions id be careful and do A LOT of homework. DIY is great and you may pull it off but get the correct process and information involved so you dont waste your time and materials. These forums are loaded with bad information more added daily.

Thanks everyone for your comments. I decided yesterday to go with real marble for my master bathroom. In case it helps anyone who are in the same boat, here are my reasonings: 1) we live in our condo currently while our house is being built. Our condo has 2 full bathrooms with entirely marble floors, shower surround and countertops. We have been here for almost 5 years, never sealed or did anything different or special while using them (mostly out of ignorance. I never knew I had to treat marble any differently until I started buying tiles for my house). We have had guests use one often and cleaning lady clean our place. We use green products because we have kids and pets - no idea whether it is good for marble or not, but don't care at this point. We care more about our kids and pets. The marbles on the floor and counter (horizontal surfaces) are not in perfect condition, but I wouldn't say they are ruined by any means. I also know now that they can be refinished to look like new when I'm ready to sell our condo, so no big deal to me. The vertical surfaces (shower surround, walls, etc.) are still in fantastic condition. That's for 5 years with no sealing or special treatment. 2) After thinking about it, I think the amount of maintenance for marble is pretty hyped up, because of point #1. It's a bit unfair to expect to have no maintenance for any flooring you have, even porcelain. And as far as maintenance is concerned, sealing marble once a year is pretty miniscule as compared to other things related to the house. For example, your lawn need to be watered and mowed way more, but does that mean you shouldn't have a lawn or put in astroturf? My family and I are pretty laid-back and will not stress over etching or slight stains, because marble can be restored. So, if necessary, we will just restore it. However, seriously consider whether you will be stressed, and if you will, then maybe pass on marble. 3) The homes in my town are definitely still using marble in their baths, kitchens, foyer, etc., including the new constructions. So, really I think it's probably not that big of a deal to have it. People are still choosing it all the time. I have not had any concerns until I started tile shopping and reading about it online. Having marble in a home is a selling feature for homes in my area, not a decrement. It's highlighted in listings. Of course, I know not all buyers care for it and might even turn off ones who think it's high-maintenance, but it's not a concern at the moment. I like porcelain tiles for many reasons as well. I will be using it in my kid's bath (not faux marble-look, something more contemporary), and in other areas of my house. For me personally, I think having the look I want is more important. It's something that I have to use and look at every day, so if I'm not happy with the way something look, no amount of easy maintenance will make up for it.

The key to a "waterproof" floor isn't the tile, it is the prep of the floor and install of the tile. By a pro. As to "cracking" tiles. That is a function of a LEVEl floor, prep, and install of the material. The floor of your bath, is a far lesser concern than the that of your tub, shower or both if your shower is within that tub. A new bath is a marriage of elements, floor , bathing, storage, plumbing fixtures, etc. Get very reputable labor. THEN........let me add that you don't flood a bath floor with water. I get no more water on the bath floor than splashes from my kitchen sink doing dishes. The shower is a different story : ) Skip the LVP, get a nice tile you like, and a pro.