We are planning for mid-October, arrive on a Sunday evening and leave sometime Wednesday late morning via train to Vienna.
Of course the Four Seasons will be the higher priced by far. Budget is not the concern -- location, nice rooms (not cramped), cleanliness, and service are the key criteria. About 20 years ago for business I stayed once at the Marriott and once at the Intercontinental and thought both were fine, and a good location for the sights we plan to see.
The Parisi looks beautiful; it is a bit further from the river bank than the other 3 I list.
Thank you!