I'm really leaning towards putting Thomas on Porter. Porter has no post-up game at all and if the Wizards try to force feed him with post-ups it will be change their entire offensive game. If the lineup remains status quo then that would mean:
Green - Morris
Thomas - Porter
Horford - Gortat
Crowder - Wall
Bradley - Beal
This is a huge problem, since unlike the Bulls series, we can't hide Green on anyone. Ideally you would want him on Beal, but Green would get torched off screens with his poor IQ. Crowder on Wall is also an issue, but that has more to do with how much Green scares me defending either of their guards.
Which leads me to my ideal starting lineup, and one that has Smart starting. I know Stevens likes having Smart come off the bench. However, the Wizards bench is pretty awful and I don't worry about having to defend Bogdanovic or Jennings. Instead I'd rather go with our best 5 from the jump. Especially against the Wizards who will be playing Wall and Beal about 40+ minutes each. So my starting lineup would be:
Crowder - Morris
Thomas - Porter
Horford - Gortat
Smart - Wall
Bradley - Beal
I prefer to put Smart on Wall since he can play off him and go under screens. On the other hand, Beal is their best offensive weapon and Bradley has been better at stopping him that Smart has.