Not the "best" but perfect for kids. Go to Garfield Rd in Dedham. Huge light display in a residential backyard that has been going on for years. They let you walk around their yard and sometimes have hot chocolate out. I think they even have a day where Santa comes. It's free but they have a donation box at the entrance.

There's also a house in Hyde Park on Meadowview near the dead end that has a legit professional lights display on the front of the whole house. It's like one of those videos where the lights sync to some shit like Party Rock Anthem, tho I don't think this place has music synced up.

Not sure if they are up and running yet (moved out of the city) but they were there last year.

Edit: Tyndale St in Roslindale is also decked out every year. We used to park next to Fallon Field and walk Tyndale with kids