What does a proprietary annuity mean. Are they really better and if so why?

It is difficult to answer this questions without having some context and making assumptions.

Did you hear the term "proprietary annuity" from someone who is working in selling an annuity to you?

If so, some financial advisors and insurance agents may have access to annuity products that have unique features that may not be available to all financial advisors.

Insurance companies will sometimes distribute their annuities through what is referred to in the industry as an "independent marketing organization (IMO)".

IMOs are basically marketing organizations.  They seek to develop a group of financial advisors / insurance agents who are interested in selling the annuity products that they make available. 

IMOs are most common when dealing with fixed and fixed indexed annuities.

At times, an insurance company and an IMO will work together to create an annuity product that has some unique features and may not be available for sale outside of the IMO's network of financial advisors.

This may be what has been referred to as a "proprietary" product.

Regarding the relative merits of the product, you should ask the advisor who is pitching the product to provide a clear and objective comparison of the product features.  Which features, specifically, make the product unique and how/why are those features better than what might be available in the broader market.