If you have never taken an ADHD child to church and you're thinking about it... plan well! Some families have made regular church-attendance a part of their routine but even if it's a routine, it isn't easy with a bouncing, darting child in a place of worship. I do not recommend "dropping off" this child in a kids' class and walking away. Get to know the teachers just as you would in his/her school classroom. And, in all fairness to the teachers, let them know about your child's special needs. Often times church division teachers do not have a lot of training or experience working with kids with high needs but they are wonderful teachers. Your child needs to feel successful or he will not want to return. If he or she is unsuccessful and always in trouble for a long period of time your child may never want to enter a church again. This really isn't what you're going for!
Some churches are more formal than others. One isn't in general better than the other, but for the ADHD child, less formality might be better. Don't be afraid to let trusted people in on your need for help with your child. These people will offer high-fives, smiles & greetings when others may be so overwhelmed they can't engage him. The less formal congregation may even allow this child to carry out roles traditionally offered to adults...ie helping out in the service.
Stay with your child as much as possible and consider taking along a good book or quiet activity your child enjoys as well as a small snack (non-messy one & only if it's allowed). These things will occupy time and keep child calm during your worship experience. (Also keeps him from dropping things from the balcony & running through the baptistry!)
Change is difficult but if your child isn't successful in church it might be time to re-evaluate his needs and match them up with the right experience.