Then use Braintree for cards and Stripe for ACH.
ACH is cheaper than cards, but it's also slower and has a limit of $10,000 per transaction [1]. Cards have a limit of $1 million per transaction [2], which is 100x bigger than ACH. Also, people are used to paying with cards.
[1] https://support.stripe.com/questions/accepting-ach-payments-with-stripe
[2] https://support.stripe.com/questions/what-is-the-maximum-amount-i-can-charge-with-stripe