What's the easiest and cheapest data roaming for travel to China?

Get a prepaid SIM card, you can choose the package you want & avoid unwanted ‘accidental’ roaming charges.

1) ChangiRecommends ( https://www.changirecommends.com/deals.aspx?cid... ) where you can pick up before departure at airport

2) just approach a store locally to purchase and get the staff to install & test for you.

3) For post-paid plan, you can also purchase roaming data plan add-on from your telco e.g. I help my mother to subscribe a roaming plan from Singtel so she don’t have to change SIM card.