1. Shanghai
-before Zhabei (historically poor district) annexed Jing'an (one of the most desirable districts), a Jing'an address = good location
-but, these days, a lot of the hotels that feature Jing'an in their names are actually in some pretty shabby areas...though new metro lines are helping to offset this
-anyway, I can endorse the Courtyard "Central" because the Hanzhong Road subway station is quite convenient, and the local area isn't so bad (e.g. WPP has a lot to do with this)
2. Beijing
-I agree with 889 about passing on the Aloft Haidian unless you have a reason to be up there
-since Beijing is so big, I suggest you focus on a few areas (e.g. SLT, Guomao, Gulou, Wangjing, downtown), and maybe post a list of candidates here (include non-Marriott options as well)
I need to think more about Hangzhou, and Guangzhou. Will try to post ideas later.