The Four Seasons is BY FAR the best choice of the three, but it's not conveniently located to Chiyoda-ku. In fact, it's just not conveniently located. The Imperial and the Palace are nice hotels, but just aren't in the same league as the FS... they are in much more convenient locations, though.

Marriott doesn't have a lot in Tokyo and by the looks of it the only one convenient to your office location (and public transport for your weekend explorations) is the Renaissance Ginza Tobu.

Given the above options I would check to see:

1) what the rates are at the Rosewood Seiyo Ginza.
2) If your company has a corporate rate at the Four Seasons Marunouchi.

On the other hand, I've been told that I have expensive taste