Three times I've stayed at one of the four hotels (AC Marriott, Hammer, Königshof, and Schottenhof) just across the Bahnhofplatz from the Mainz Hbf. The first time, 1988, there was a chain restaurant, Wienerwald, right on the Platz, but it's no longer there. My third time, in 2008, I thought there was a lack of places to eat in the area (I waited until late to look, and the restaurants in the Hbf were all closed). Looking at Google maps, it appears that there are now a variety of places, from very nice restaurants to Kabob kiosks, plus many places to get food in the Hbf. Hotel Königshof, where I stayed in 2008, has comfortable rooms, a great breakfast buffet, including American breakfast food, if that's what you want, and is conveniently located minutes from the Hbf, from which the S-Bahn goes to the airport in 26 minutes every half hour. There are also several regional trains to the airport every hour.