I haven't stayed at the Messe Sheraton but have used all the others.

Only the Airport Sheraton has a Towers Lounge with drinks/food but they get a bit iffy about extra guests if a) not staying in a Towers room b) said guests aren't SPG members.

Be warned that Frankfurt prices go through the roof if there is a big Fair on like the motor show.

If you are flying in, overnighting and going to a meeting before flying back out, the Aiport Sheraton is very convenient and is attached to the airport T1 by a footbridge which then goes onto the the long distance train station.

Otherwise if you have more time, go for LM or the Westin to be in the centre of Frankfurt.