I started with OpenSEF and after being abandoned, jumped to JoomSEF until the spam tags appeared. Then I used the Kangainternet JoomSEF mod until I found sh404SEF, which does everything the others do, and a lot more, see the supported components list. sh404SEF is faster (with caching!) and easy to use just like JoomSEF. Then I dabbled with SerrBizSEF. I'm back to sh404SEF now, and I can tell you that I won't be messing with any other SEF extensions for a long time. This one is by far the best. Thanks to the developers for an amazing product!

I downloaded the free version for testing, and the next time I tried to log in to serr.biz my account was blocked. The actual extension appears to be a cut-down sh404SEF component, and you have to pay to enable the features that come with the regular (and free) sh404SEF component.
I'm just hoping this SEF extension isn't as fickle as the developers.
I give SerrBizSEF v1 a C+ for being a light-weight stand-in for sh404SEF. It's OK for now. Thanks.

Impressive, full quality extensions. It's not as speedy as Open-SEF but it will work with Virtuemart. In my books that makes it a winner. Download now. You'll thank yourself later.

I haven't tried it on IE but it's smooth on Firefox 1.5 and 2.0. Check the demo.

I found that this Joomsef component, by itself, generates 25 queries per page on my personal website.
In comparison the OpenSef component generates 3 queries.
That's a huge difference, and Joomsef doesn't have nearly as many options as the amazing openSef does.
Conclusion: JoomSEF is required if you're using JoomFish but otherwise, you might be best served to steer clear.

The good:
-easy to set up
-easy to use
-nice tutorials available on developer's site
-form validation, lots of features
-it works!

The bad:
-limited choice of themes

This is the forms component for people who need basic Contact or simple forms. It's easy, powerful, and if it doesn't do what you need, then you'll be wanting to use FacileForms or Fabrik. Good luck.

This one was tricky - I first tried it at 1.1.7 & several MAJOR features weren't there. The other options (VirtueMart, OScommerce, Zen-Cart, Drupal e-commerce) didn't have my features either.
I rate ECJC highly because it's basically got everything I want. I might switch to Virtuemart later but for now, ECJC is the best.
- Lots of shipping/payment modules available. Most templates work fairly well *though a couple RT themes present troubles*
-There's a good community surrounding ECJC and the "commercial" license isn't onerous, it's open source and $15 to disable the ads.
-The developer seems pretty responsive to support queries. I'm eagerly awaiting 1.1.9 to put into full scale production, it allows customers to purchase without an account.

Note: VirtueMart 1.1 will have purchase-without-account functionality too!