Ralph,in response to your Times Square choice:
We have stayed at the Marquis quite a bit over the last couple years, and here's my opinion (full disclosure: I have not stayed at the Renaissance)
As a Silver Elite you'll more than likely need to pay extra for the luxury floors at either place--but the regular amenities at the Marquis are nice. One downside is the sometimes slow pace of the elevators, which apparently are better than the bad old ones.
Stay at the Marquis, use the concierge in the lobby for help, and have a great time. Split a Junior's cheescake--best one I have ever had
The two properties are very different. The Renaissance is kind of classy but the rooms are tiny while the Marquis is absolutely MASSIVE and a madhouse. I checked into the Marquis for the first time last December and was given corner room, which was very large. The Concierge Lounge at the Marquis was well stocked but very crowded and one day when I arrived at 9:25am I found that they were already closing up shop and all that remained for breakfast were various breads.
In the end I think the choice between the two is a very individual thing, but I think the next time I visit the city I will check into the Renaissance. If for nothing else, it's peacful.