This is not really helpful. As others said, it depends what you are looking for. The Westin is just another Westin (one of the better ones), the LM is (when you stay in the older part) a pretty traditional place. Locationwise they are comparable - walking from the Westin to the LM might take you 15 to 20 minutes. However, there is plenty of wisdom on the forum, there is plenty of wisdom about Frankfurt in the German Forum and everything you need to know about trains in the European Train Forum.