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You will need a job offered to apply for Visa 457,
If he is likely to get the state to sponsor, i would say go for 190 which is state nomination.
If he has enough points, 60, it is even better for him to apply for 189, skilled independent, so you can live in any part of Australia you desire.

thanks for the reply.

He has enough points but the last job he has since the past 2 years (ICT project manager) is not listed in the list for the 189 visa. I understand that only job experience for the past 2 years is relevant. Am I correct? Although he was software programmer or ICT business analyst a few year ago and these are listed for the skilled independent. So I'm a bit confused whether he can apply for the skilled independent visa 189.

Otherwise, I was thinking about 190 (state nominated, for which his job is listed as high availability in some states) and 186 (employer nominated, direct entry stream). Which one do you think he has more chance to get a nomination?

I just got my 189 approved and i stopped working after i become a mom in 2011. 

Please refer to this, whatever relevant work experience for the past 10 years is taken into consideration. He can go for an occupation that he has spent longest time in.
You will need certain documents to prove what you claim, eg, job offer letters, reference letters from the companies you previously worked with, etc.
Good luck!