The only thing you can find online is usually catering to rich western tourists or "expats" and usually boils down to "Which place is the most western/ High GDP and McDonalds!" so I'd rather get an opinion from someone that's been there that isn't a business tourist.
I did have friends who lived in the suburbs between SZ and SH and commuted daily to SH, so its current economic influence can definitely overshadow the historical relationship between the two cities.