The Westin has one obvious advantage: it has a lounge, which the LM has not.
However you can't really beat the LM location. It's right next to main station and just a short walk from major places like Karlsplatz, Odeonsplatz, Marienplatz, Sendlinger Tor, etc.
The bathrooms are about even, but only really large in a suite, which is hard to get in both hotels, due to the large number of business travellers (which are mostly Plats) that stay in both houses. Parking is possible in both houses, though easier in the Westin. But as was said earlier, you don't really need (and want) a car in Munich.