For existing Heroku projects, I chose Render. For newer projects, I mostly use Fly.io. It also depends on a few more factors like Postgres need of the project, in which case I choose Fly's managed services. Fly.io also makes it easier to deploy docker based projects. Render is more like plug-a-GitHub-repo-and-play.

Bear in mind that I'm only comparing these too in terms of their free tiers.