Is it better to stay in Guangzhou or Dongguan dongcheng district for shopping and sightseeing

Both of these two places are ok for you to go shopping and sightseeing.
In Guangzhou, you can go to Yuexiu Park, Pearl River and White Cloud Mountain. And to tourists, the city is really a 'Shoppers' Paradise'. Shangxia Jiu Lu Pedestrian Street is a good choice for you to go.
In DG, Humen Bridge & Naval Battle Museum and Opium War Museum are attractive scenic spots. And you can go Nancheng Fumin Commercial Pedestrian Street to buy clothes or shoes.
Comparatively, Guangzhou is much suggested.

Thank you so much Guangzhou it is. Any suggestions if it us better to go from HKG airport at night by by strain or ferry we get in around 2000

So you are traveling from HKIA to Guangzhou? If so, the direct cross-border coach would be a better choice as you land around 20:00. The coaches to Guangzhou operate till 22:15.