We recently had lots of light colored porcelain tile installed throughout much of our downstairs. The light grout looked the best, so that's what we went with. I spent weeks researching grout sealers and got samples of a couple of them. The one our tile store recommended was useless in a test run. I finally ended up buying a product by Dupont called "Bullet Proof Grout Sealer". It's expensive, but so far it is holding up well with several pets and people who drop stuff on it.
I had a hard time finding the stuff and bought the first quart (it took 2 quarts with much left over for 1100 square feet of grout.) and bought the first quart in a tile store in the next town at about $56. I bought the other quart from Amazon. The cheapest place to buy it, even with shipping was Amazon.com, believe it or not. I see that they now have it on Prime shipping, so if you have that you get free 2 day shipping. I posted a review of it here:
http://www.amazon.com/review/R2FIKP...065W8G8&nodeID=&tag=&linkCode=#wasThisHelpful I've only had it down for about a month, but so far I'm happy with it. Liquids bubble up and don't seem to sink in. I'm not sure what would happen if you left something like red wine on it for hours, and not sure if anything would hold up to that.
I think applying grout sealer, especially when you have a lot of it is one of the most tedious jobs there is. I did it in sections as the tile was being installed. (After waiting 72 hours for it to cure.) Hope this helps.