* Peter Pentchev <roam@ringlet.net>, 2016-04-06, 17:33:
Yep, that's part of the reason I updated to debhelper 10; please see the changelog of debhelper-9.20160402 and 9.20160403 :) Still, there are some packages and weird architectures that need autotools-dev *in addition to* autoreconf; see e.g. https://bugs.debian.org/766734 in mbuffer.I prefer autoreconf instead of autotools-dev
If your package uses Automake, then autoreconf will call automake(1), which updates config.{sub,guess}. Then you won't need dh-autotools-dev. In fact, autotools-dev's README.Debian says that you should not use dh-autoreconf and dh-autotools-dev at the same time.
mbuffer doesn't use Automake, which is why the use of dh-autotools-dev was needed.
-- Jakub Wilk