Hi,
I would advise that you go for the Direct Entry PR, if you are eligible. The Vetassess skill assessment requires a degree, and a given number of years of work experience (depending on the relevance of the degree). The 186 visa application requires at least three years post-qual work experience.
The Direct Entry will cost a bit more, given the skill assessment, but leaves you less vulnerable to Immigration changes (or a company downturn and possible redundancy on your 457 visa in the coming 18 months).
If you are choosing an agent, do you research in terms of their reputation online, experience and see if they offer a No Visa, No Fee. True Blue's fee to manage your case would be under $4K.
Joy