We use Stone Tech for all of our sealing and cleaning. I have used Miracle products for many years and have found them to also be very good. We went to Stone tech primarily for the fact that they have very knowledgable people a phone call away..Real customer service is a big plus when your dealing with chemicals.
For general sealing..like your travertine..we use solvent based impregnators. Stone Techs Impregnator pro is a great one and is simple to use. From Miracle sealants I would use 511 or 511 porus plus. I think Stone tech's chemical make-up offers superior stain protection compared to the silicone base in the Miracle 511...so in the long run you may get more "bang for your buck" with the Stone tech..but that's my non-chemist "real-world" expirience