A Solo 401k is generally a better choice than an IRA as long as you are eligible. Are you self-employed?
There are some advantages to the Solo 401(k) as compared to a comparable IRA. The elimination of taxation on leveraged rental income is one, but keep in mind the tax impact in the IRA is nominal. Wedging into a Solo 401(k) that is not a truly good long term fit just to avoid that taxation is for most investors a losing proposition.
Plan qualification and determination of which plan is best for a particular investor, their situation, and investment goals is certainly not a one-size-fits all topic, and there is no one right answer.
The #1 consideration with the Solo 401(k) is current and ongoing eligibility. An IRA is an individual retirement arrangement, and quite permanent by nature. A Solo 401(k) is a qualified employer retirement plan, and needs a legitimate business activity with no full time employees to act as a sponsoring employer.
You can read all day long on BP and get into paralysis of analysis, as well as digest some less than accurate information on the topic, to be sure.
Alternately, you can read up a bit, with the goal of identifying a few professionals in the field, and then get on the phone. You will learn much more, much faster that way, and should be able to rely on the quality of the information provided.