The Sheraton at FRA is very very close to:
http://www.thesquaire.com/
The Congress is right in the middle of a major office building suburb of FRA, actually more or less directly opposite of Nestle HQ Germany. 2 stops with a regional train and 800 m by foot or two stops with the tram.
The Westin is 50 metres or a closed back entrance away from the high street in Frankfurt, the Zeil. Most of the stores there are the highest grossing ones of their brand in Germany, so you are in the middle of a shopping heaven.
The LM is 200 metres away from a side entrance of the railway station...and two-three tram or trains stops away from the shopping mile mentioned above
If you do not have status with SPG, I do not recommend the LM, their smallest rooms are ~ 10 sqm.
Westin is the best SPG property in town, no doubt about that, Sheraton at FRA is a good second choice, the other three properties are nothing to write home about and have quite some potential for a mediocre stay.
Even on a good day with a suite upgrade, you will not tell your grand kids about a stay at the Congress, Sheraton Offenbach or LM Parkhotel