Scouting for the best
One really can’t name one product as the best grout sealer. Depending on what you are using the sealer for, there are a large variety available in the market. There are different ones for granite and for marble. The one’s used for tiles that are laid down in the kitchen and restrooms too vary.
Among the best grout sealers are the following – Stone Tech Sealers & Cleaners, under this brand name is a product titled Bulletproof and this has by far garnered the best response. The only drawback with the product is that it has to be shipped to you and many people do not want to wait for that long. 
The brand Tile Labs have come out with a product titled Surfacegard. This comes fortified with DuPont Teflon and comes with a 20 year written guarantee. A product can’t get better than this.
Next comes AquaMix Sealer’s Choice. This is a popular choice among all those who like to do their work themselves. There are rarely any complaints about it on the online networks. It follows close on the heels of Bulletproof in terms of quality and value for money.
Another product from Aquamix is Ultraseal. This comes at a decent price, but there are several warnings on the product itself on the short life span that it has. There is no real mention of a warranty. The customer service for this company is worth mentioning. The same product is also available under a variety of names such as Superior Premium Gold and this is available for a variety of tiles such as granite, marble etc.
Another product you could consider is StoneSpecifice from Custom Building Products (CBP). You will have to do a bit of research however on where the product is locally available for you. Miracle 511 and its products such as 511 Impregnator, 511 H2O as well as the 511 Porous Plus are also considered good value for money. The task is just to find them locally.