I find Echo more complicated and more difficult to style. A bunch of what seems to be older legacy code is running around, their help and tutorials are complex and sometimes difficult to follow. They also seems to have slightly slower page loads, and deliver more javascript and objects. However, with the complexity comes more power and more options. They do require some payment, but this also gives you better sign-on options, ability to remove their branding etc.
Disqus feels cleaner and the because there are fewer choices it is simpler to use. Overall it feels lighter weight (in a mostly good way). However, the reduction in options means that if it doesn't do exactly what you want out of the gate, it may not be possible to do what you want at all. Single sign-on and white label requires you to contact them -- pricing is not public on their site.
I have had difficulties with both with regard to Facebook login (post OAuth 2.0) but I expect both to resolve these shortly. Tech support has been responsive for both (both unpaid Disqus and paid Echo).
Integration for both into wordpress was mostly ok, though there were a few bugs with migrating comments inside of Echo it wasn't anything too difficult to address.
In short, I would say I would use Disqus where you prefer a free, simpler, easier to manage solution, where you do not need to white label (remove disqus branding), don't require or don't mind multiple logins (logging in to your site and also to disqus).
Use Echo if you want more options, greater ability to customize, the ability to white label and to do single sign on.
In both cases you will need to do extra work to get SEO credit for blog comments and deal with occasional network slowdowns. You also have to live with their time lines for rolling out updates and features. If commenting is core to your site you may well want to bring it in house, otherwise either of these products work well.
I use Disqus for my personal blog. They are really cool people and they're users here on HN. However, I've had problems with Disqus not showing comments after a few hours, and I've since read at least one other blog that has had the same problem. I'm sure it's something they'll fix eventually so I wouldn't necessarily let that dissuade you. I don't have any experience with any of the other comment systems.
It does get frustrating when you have an article with 40 or so comments, and only the last two visible. I like Disqus a lot, but if it simply doesn't work - it doesn't work.
There are more comment vendors than those three, but I use DISQUS. Some blogger friends use intense debate and comment luv. Both of those comment platforms seem to be gaining steam, but i am partial to DISQUS
I've been using js-kit, or Echo as it's called now, since they first came out a few years ago. They've had some problems before (slow loading, delayed moderation), but they've been good lately.
I like that you can style the comments almost any way you want them with custom css. I like the analytics they give me, and the fact that they're pretty versatile with what they offer (custom html, video/picture embedding). Of course there's also the social aggregation feature which is pretty cool if you find it useful.
DISQUS seem to be wanting to cater to the long tail of blogs, JSKit/Echo is looking to super-serve "pro publishers" (they power comments on a lot of news websites, etc)
I like what Echo is doing but if it is just for a small blog you might find it overkill, plus I believe it isn't free.
However, the feature set is interesting.
As it happens, I don't use either on my blog. I don't see much value add in the end.
I use Disqus on my personal blog. (I've never run a big news site before, so I have no idea what their needs are.)
I use it because I like to pull in the retweets as 'social proof.' My users aren't very good about commenting (which is sad, because I have call-outs and everything), so any social chatter I can pull in makes a richer, more interesting site.
I've used Disqus in the past but switched back to plain WordPress comments because proper theming was almost impossible. I used CSS overrides to hide elements and make them fit the layout, later they changed some code and I had to do it all over again. Changing the path of my blog also caused problems.
Livefyre.com - I work there as an intern this summer and I really like the system. You have to sign up for the beta as we're still rolling out, but should be quick.
I find Echo more complicated and more difficult to style. A bunch of what seems to be older legacy code is running around, their help and tutorials are complex and sometimes difficult to follow. They also seems to have slightly slower page loads, and deliver more javascript and objects. However, with the complexity comes more power and more options. They do require some payment, but this also gives you better sign-on options, ability to remove their branding etc.
Disqus feels cleaner and the because there are fewer choices it is simpler to use. Overall it feels lighter weight (in a mostly good way). However, the reduction in options means that if it doesn't do exactly what you want out of the gate, it may not be possible to do what you want at all. Single sign-on and white label requires you to contact them -- pricing is not public on their site.
I have had difficulties with both with regard to Facebook login (post OAuth 2.0) but I expect both to resolve these shortly. Tech support has been responsive for both (both unpaid Disqus and paid Echo).
Integration for both into wordpress was mostly ok, though there were a few bugs with migrating comments inside of Echo it wasn't anything too difficult to address.
In short, I would say I would use Disqus where you prefer a free, simpler, easier to manage solution, where you do not need to white label (remove disqus branding), don't require or don't mind multiple logins (logging in to your site and also to disqus).
Use Echo if you want more options, greater ability to customize, the ability to white label and to do single sign on.
In both cases you will need to do extra work to get SEO credit for blog comments and deal with occasional network slowdowns. You also have to live with their time lines for rolling out updates and features. If commenting is core to your site you may well want to bring it in house, otherwise either of these products work well.