Opinions Please: Best Conversion (eg, Landing Pages) Plugins for WordPress

I am researching plugins for WordPress. Any opinions you may have would be greatly appreciated.

What are your thoughts on the following conversion plugins for improving effectiveness of landing pages?:
* Wufoo
* Contact Form 7
* Hubspot (paid)
* Premise
* Gravity
* Optimized Press

What experience have you had with these? Reliability? Ease of use and maintenance? Security concerns? Effectiveness?

Are there others you would recommend instead?

Many thanks!