They all lack on one point. Schnack: Requires Github or Twitter account it seems (not everybody who comments has a twitter account). Isso: In princible ok too paranoia (strange icons, no Gravatar or any log in at all). Commento: Does not know how to handle links in comments and no login system.
So they are all ok but far away from a Disqus alternative.
There's also EffectiveDiscussions (https://www.effectivediscussions.org), which doesn't have any of those drawbacks. It has email+password login, Gmail, FB, GitHub. Open source, and hosted too, if you don't want to provision your own server.
Agree. I would like open source + hosted version. Really simple hosted version for a couple of $ so you can have it on personal/project pages. There is of course disqus today, but never liked their ads, and of course its lock in.
Seconded. Disqus is bloated beyond repair. Open source + hosted is a fantastic model for consumers and entrepreneurs, and the hosted money would be enough to get rid of advertisements.
GitHub: https://github.com/debiki/ed-server. It's more lightweight: the script bundle is just 140kb in comparison to Disqus 750kb. (I'm developing it.)