This is by far the best form out there. I've tried others and this one is totally worth it. Easily customizable and great for complex forms as well as just simple forms. There were a few bugs when I got the new version for 1.5 however the support is top notch. I would receive multiple responses within hours. Definitely recommend this.
This is an excellent plugin for Joomla. It leaves unlimited possibilities for php developers. Support could be a bit better, but you should be able to find the answer to your problem in the forum they provide.