With email you are direct: you know who asked for your newsletter, who is receiving it (but not necessarily reading it), and you can add all kinds of formatting. The drawbacks are frustrating: Google or other cloud email providers shunting your newsletter into something other than the Inbox, anti-spam tools erroneously flagging your email as spam, email gateways sanitizing and potentially blocking parts of your rich content, and different email clients on different platforms rendering your formatted emails in unexpected ways.
RSS is its own double edge sword of content distribution. Like email, RSS is an old standard with several ways of interpreting the standard. RSS is from the source, so typically no third party provider is needed to offer RSS (it is built in to WordPress, for example), readers fetch the feed when they want to read it, and it is largely (but not exclusively) text based. Formatting control is limited but by default feeds will be truncated to “encourage” users to visit the site for the rest of the story.
As with many things I think content creators should offer different avenues to get at the content – RSS, email newsletter, social media, Apple News, etc. So long as the maintenance overhead is low (not like Apple podcasts, which is painful) and the costs are manageable, deliver the news where your users live.