Chen Yan, a 32-year-old native of Wuhu city, Anhui province, said he worked in Beijing and Wuhan, capital city of Hubei province, from 2007 to March of this year, when he returned to Shanghai, where he worked as a painter for five years.

"The social welfare framework is more complete in Shanghai. I'm involved in social security policies in the city, but no employers elsewhere offered me that," Chen said.

The Social Insurance Law, which requires all individuals to be included in the social insurance system, took effect in July 2011, but experts said it was not put into practice in some places.

"Moreover, migrant workers sometimes get lower pay than what was promised, and tardy payment still exists in some provinces," said Gu Yueming, deputy director of the Shanghai SME Development and Service Center.

Salaries for migrant workers are not higher in Shanghai than other cities, according to figures collected by daguu.com from employers nationwide.

"Salary alone is no longer the main factor to migrant workers. What they think highly of is the long-term development of work opportunities," said Zhang Biao, executive of Shanghai Minjie Labor Service Co, which has been in business for more than 10 years.

"They are more willing to take challenging but promising jobs rather than repetitive manual work that demands overwork and may get them decent pay," he said.

The younger generations require a better work environment and living conditions than the older generations do, according to Zhang, and some businesses in Shanghai meet the younger workers' expectations.

"Some enterprises encourage workers to place the picture of their boyfriend or girlfriend in the locker rooms, because they believe married people work for their children, but unmarried ones work for their future marriage."