As a consumer, and lead on a team that has contributed in the past, I place my vote squarely on GitHub Issues. It works well and it keeps the issues closely aligned with the code. It's also easy to browse and follow comments. Minimalism is good in this case. From a consumer point of view, it's a bit off-putting to have to go to a different site where I need another login to be able to browse through issues. I've never found Bugzilla good for browsing.
I like to be able to see the state of a project, what's aligned against milestones, and who's been working the latest issues. The project seems much healthier and much more open when this is the case. Since the migration to LocationTech, we haven't been able to get a sense at all of where the GeoGig project stands or how close (or not) it is to a release. When we had issues in GitHub, it was much more transparent. The fact that the code is in GitHub is great. It's also easy enough to hook into their API for Issues upload and download. The GitHub team helped us with the first migration we did to go from Jira to GitHub Issues.
My 2 cents: Please, please, go with GitHub Issues.
Cheers,
Scott