What is the best way to contact USCIS on I-526 inquiries?

Email the immigrant investor program office or have your attorney do so. I believe USCIS does answer all email inquiries or tries to within reasonable time, but sometimes attorneys can be more efficient because they know exactly what information USCIS needs and have dealt with them before.

One-on-one face meeting has been suspended since March 18th. E-mail may not be effective at this time, considering the COVID-19 at this moment which has resulted in employees operating from remote sites, Therefore, you should consider telephony contact and using your attorney may help.

I think email is best. I would not expect them to give preference to an attorney if you are the beneficiary.

I have not noticed a difference between an attorney contact and an investor one. They prefer you to start with their egov tools on their web site.

The only way to contact IPO is via the email address: USCIS Immigrant Investor Program.

Email is the best way. Having email access to USCIS is one of the privileges EB-5 investors enjoy. USCIS responds to all emails whether those are sent by the petitioner/investor or attorney. I suspect attorneys are better skilled at drafting emails in order to receive the info they seek from USCIS.

Submit a case status inquiry through their case status online portal. Both have the same chance of being responded to.

Email is fine. USCIS responds to the public the same way they respond to attorneys.