CP/485
There is also the option of the AC-I140 (Attorney Certified) CP. Some consulates like Mumbai , Delhi , London , Montreal permit this. This is a faster process.
The downside to CP is that you are out of the country and have no right to contest , if your Immigrant Visa (GC) is rejected. Also , if you are to lose your job during this process , that could be an issue.
There are a lot of postings on Consular Processing in this forum.