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.
So they are all ok but far away from a Disqus alternative.