There are many bad arguments against Sola Scriptura. There are many terrible arguments made to suggest that none of the early church fathers taught or practiced Sola Scriptura. But there is, in my opinion, one worst argument.
That worst argument is this:
1) Reformed apologist demonstrates that early church father X taught Sola Scriptura.
2) Person opposed to Sola Scriptura responds: Oh, so you think that ECF X got "Y" from Scripture alone? Where "Y" is some belief allegedly held by ECF X, but one that we don't accept.
3) The enhancement of this terrible argument is when it turns out belief "Y" is not actually what ECF X taught.
4) The further enhancement is when the person opposed to Sola Scriptura elsewhere makes the claim that Sola Scriptura leads to doctrinal diversity.
There are several ways we can respond:
1) We can point out that just because we have the same rule of faith doesn't mean we agree on every single doctrine.
2) We can point out that there is no logical connection between Sola Scriptura, as such, and doctrine "Y".
3) We can ask the person to try to demonstrate to us how ECF X got doctrine Y.
We could also
* dispute that ECF X taught "Y", where appropriate (obviously, if they did teach Y, then this is not an option), but that gets the argument off on a tangent (which may be what some of the folks who use this worst argument may hope);
* point out that the ECFs were not perfectly consistent with themselves (sometimes they contradicted not only other ECFs but also themselves); and
* ask what alternative to Sola Scriptura they think the particular ECF actually practiced/believed/taught (this is not a direct rebuttal, of course, but it does provide an opportunity to learn from the critic - after all, it is possible that our claim was mistaken, as God nowhere promises that all the teachers of the church will teach all the truth all the time).