How do I contribute patches to packages (GitLab merge requests or diff -u + bug report)?

[Vishal Subramanyam <vishalsubramanyam@outlook.com>]

Hey,
I wish to contribute patches to Debian packages, but I am confused
about how I should go about doing so. The Debian Handbook says that
using GitLab might make it easier for maintainers to merge changes, but
somebody on an IRC channel told me that the old email-based workflow is
still the dominant way of delivering patches to developers.
I find it easier to work with GitLab. What should I do? Should my
preference depend on the package maintainer's preferences?

Vishal