Is it relevant experience? Many of the MAS job ads, I see they indicate DD/AD.

Yes, all my exprience is relevant experience in other stat boards. I applied a few MAS positions last year. One is AD/Associate. Rest of the positions are DD/AD. All applications status become "In Progress". But the position (AD/Associate) is the first one to call me for interview.

Don't know how MAS give the rank. A friend, who is Senior AD in a ministry, applied MAS but offered only AD. Senior AD in other stat board and ministry is considered quite high rank, as most stat board DD is division head level. MAS AD is low rank.

Try procurement division under corporate. Hahaha

One staff is DD two year contract. One staff is AD perm. Which one is better in your opinion?
The DD two years contract is recruited under sgunited contract.
Guess it depends on individual whether they are more concern with the rank or perm

Corporate Security Division

Hi. Better for you to leave after two years. Treat it as a stepping stone

At the end of the day, if MAS offers a higher package, then the title doesn't really matter. Rather be a "low ranked AD" earning 10k then a "head" earning 8k.

10k is more like upper range of DD's pay.

The pay of DD, you referring to, is from MAS or from other gov agencies?

This is impossible unless your friend is directly headhunted for very deep expertise in a certain field.