The only Starwood property I have stayed at in the area is the Arabella Offenbach. I was quite pleased with the quality of the rooms and the public spaces, including a good breakfast buffet included in my room rate.
I found it very convenient for getting to the Messe--I don't remember if it was a direct train to the Messe, or if you had to transfer across the platform at one of the stops, but it only took about 15 minutes and went right to the Torhaus in the middle of the fairgrounds.
Also I liked the surroundings in Offenbach, with some decent choices of restaurants within walking distance--more convenient for dining than many areas in Frankfurt.