Both properties typically afford platinum guests with suite upgrades. On that basis, either one is quite acceptable, although I personally feel that the Russell suites boast a bit more character. In fact, it seems to me that no two suites there are the same.
During my midweek stays, I also enjoy the fact that Russell provides a club lounge in which gold or platinum guests can enjoy a continental breakfast or early evening snacks. Please note that these snacks do not include soft drinks other than water.
The Russell also waives local phone charges for up to 20 minutes per call. That's not great, but its still about 20 minutes longer than you would enjoy at the W.
Given that you will not be able to make use of the lounge during your free Saturday, I would say that if the phone charges don't matter to you then I would choose the property on the basis of its overall ambience. I consider the old world boutique environment provided by the Russell to be more suited to my personal tastes but others would certainly find the W to be more appealing.