Honestly, I think Atticus was a perfect attorney.
If I had to try to defend Tom that day and did not want to lose, I would probably have made an effort to include more witnesses, like I would have tried to provide an alibi for Tom. But then, it might have turned more into the white vs. blacks. If he was with a black person, the crowd and jury likely wouldn't have believed the person.
It might have been good to put Link Deas, Tom's boss on the stand to vouch for his behavior as a worker. But again, Link might have done something himself to get thrown out of court.
Calling one of the other Ewell children to testify might have been a good idea because they, like Mayella, would struggle with the difference between a truth and a lie.
All of these extra people would have just been to call characters to account, I am not sure if it would have helped. I appreciate Harper Lee's order of events because they are realistic and legitimate for the time period and the circumstances.