The Georgia case is actually the weakest one. Some of the charges are technically unconstitutional on their face, and Trump's lawyers can use those to have the indictment thrown out, and if they're mean about it, they can file to have the indictment thrown out the night before the trial.
The DA in that case would then have to refile the indictment without the unconstitutional charges, and if they fail, that's it. They get two tries and then trump gets off.
Also, Georgia RICO law is a mess. That will lead to appeals where Trump might get off.
The final part that makes the Georgia case weak is that Trump can easily get it transferred to federal court, which could add years to the case before it even gets to trial.
No, the strongest case is from DC. Jack Smith did a fine job of threading the needle of not charging Trump for anything he said, just what he actually did. So no first amendment defense.
The top secret document case is also pretty strong, but the judge is blatantly biased. Which is almost impossible to prove through the official process.