I want to learn to build RIA's, however, do I build them with Adobe Flex or Adobe Air, or both??? Which one do I start learning first?
Also, which version of Flex is best? Flex 3 or Flex 4.
If anyone can give me the basics of where i should start off first would be great.
And am i right in assuming Flex SDK and Air SDK are free?
The SDKs are free and you can get them from here:
I'd recommend Flex 4 since it is the current version in production. Flash Builder 4 is the current version of Adobe's IDE for developing Flex/AIR applications. It isn't free, but there is a free trial period. There are other free options out there for a development environment but I'm not very familiar with any of them. You can check out Flash Builder 4 here - http://www.adobe.com/products/flashbuilder/
As far as where to get started, the net is full of info on both subjects and this forum is a good place to get info. You can start out getting familiar with what Flex is here - http://www.adobe.com/products/flex/overview/ and AIR - http://www.adobe.com/products/air/