Short answer:
There is no exactly perfect language.

Longer answer:
Because of several Supreme Court rulings, any satisfactory amendment language or process today must first abolish corporate personhood in order to then require legislatures to regulate campaign finance.  However, many additional principles complicate the possible amendment language.
(See: Permitted vs. Required Regulation in FAQs).

To name only a few of these bedeviling notions, free speech and freedom of the press* in influencing elections, the State's rights to regulate their own elections, the regulation of the window of time in which money can be legally raised for elections, or the now-related issues of "money-as-speech" stemming from "corporations-as-people", have each made much of the debate very complex.  Thus, it is difficult to conceive of an absolutely perfect bill.
(See: Free Speech and Freedom of the Press in the FAQs).

However, the Official National Intervention Sobriety Test (NIST) allows for a variety of concepts to fulfill the guarantee that campaigns are controlled and owned by the public interest, not the private interests (often intoxicated by wealth and power).  It does so by explicitly stating that sponsored amendment proposal language can be "equivalent in effect". 

For instance, the effect of making all campaigns only publicly-financed is to make any private interests' monetary contributions virtually insignificant. Many very intelligent people have wrestled with how to best accomplish this*. Banning all money other than public funds is one way to get this result.  Constitutionally requiring lawmakers to guarantee there will be no unfair advantages creates the same outcome, making this latter concept "equal in effect" to that of a complete ban on all non-public money in elections. 
(See: "Are Elections a Public Utility?" in FAQs).


House Bill Concepts:
Here are two US House bills that, when compared, provide an equivalent effect for elections:

Former Rep. Dennis Kucinich's (D-OH-10) bill here from 2012:
Bill "A":  https://www.congress.gov/bill/112th-congress/house-joint-resolution/100/text 
(NOTE: This bill has already passed in 3/4 of the required US states to trigger the next step in making it the 28th amendment).

Or, in Rep. Pramila Jayapal's (D-WA-7) bill from 2019, seen here:
Bill "B":  https://www.congress.gov/bill/116th-congress/house-joint-resolution/48/text 
(NOTE: This bill covers the effect of both criteria in the Sobriety Test.

In Bill A, only "entirely public funds" may finance a federal campaign, guaranteeing that no candidate has an unfair advantage and that the People always know who is funding a federal campaign; we are. 

In Bill B, Congress is required by the Constitutional amendment to guarantee "that no person gains, as a result of that person’s money, substantially more access or ability to influence in any way the election of any candidate for public office or any ballot measure".  The outcome of one bill's language on federal election finance is the "equivalent in effect" of the outcome of the other bill's language on federal elections. (Here we will not review the other differences in these bills, but see below for Q&A on "Federal, State, and Local" campaign finance considerations).  

Senate Bill Concept:
A bill introduced to the US Senate by Sen. Jon Tester (D-MT), S.J. Res. 11, provides for an amendment to the US Constitution to explicitly abolish corporate personhood, but does not require congress to eliminate advantage or influence from money in politics:

https://www.congress.gov/bill/117th-congress/senate-joint-resolution/11/text

This language eliminates the foundational basis for corporate money in the election process. The US Supreme Court has used the notion that corporations are persons, and their money is the equivalent of protected "free speech" in politics. A critical first step in free and fair elections is this exact elimination of the concept that corporations are people with any rights to influence elections. However, this bill simply returns regulation of money in politics to the US Congress; stronger language would also require that elections in the US are publicly-financed, or, alternatively explicitly prohibit any money in politics that could create any outsized advantage or influence compared to that of any other citizen.


In Summary:
So, if the two criteria in the NIST are met, or their equivalent in effect, the test-taker will still pass our sobriety checkpoint.

Continue on to "Does National Intervention Do the Actual Amendment Work, Too?" or other FAQs.