Suggestion
This is not a legal advice!
There is so-called "Priorities" for filing relative of family members. For example, filing brother or sister of US citizen falls to the lowest priority, filing married child of GC holder is around the middle priority. Check USCIS web site on "how to bring family member to the US" section. The priority is used to give quota or how many number of people can get the immigrant visas.
For your case, you need to file I-130. There are 4 major immigration office in the country with different processing time for each. You can check the processing time on USCIS web site. Based on the processing time and I-130 priority, you will be able to determine the quickest service center that can process your file.
I hope this helps. It's complex but you can find the information in the web site.