- Short answer:
Adobe flex as a framework and Visual Studio + .Net as an IDE.

Longer answer:

- Framework

Flex was doomed because flash sucks: constant security issues, slow, not correctly integrated in browsers. Apple accelerated it's death but it was doomed anyway.

I'm now a javascript dev and could not find any front-end framework that came close to the ease of use and consistent functionality that flex provided.

- Language

As for back-end stack, node.js all the way. Javascript has a lot of caveats but it's fun to work with (compared to other languages).

Java is too verbose and too objectish. POJOs ? come-on, it's almost 2014. Factory factory factory ? come-on... But the language is powerful. Anything needing transactions, JVM all the way... Java or Scala is another question I can't really answer.

Ruby is nowhere near lightweight as node (bundle install PITA, server start PITA). PHP is powerful but there is something wrong with the language (can't really pinpoint what the problem is). Python I have never used but now I tend to disregard non async language.

Believe it or not, I was a java dude and javascript hater. Now I'm a javascript dude and java hater.

I also think that Javascript/HTML are just waiting for a kick in the but and a replacement. Have you played with front-end frameworks/library ? What a piece of... mess. Only AngularJS seems ok-ish. The web needs fixing. Google is giving it some tries (Dart, Go).

You'll find hundredfolds the amount of opinions as there are languages or frameworks or libraries or IDEs. The most important is to stay curious and open minded. Don't forget to take a step back on the technologies you use. It allows to give the right advice and make the right technical decision. Most of us are wrong more open than not. When you realise you're wrong, you learn and can move forward.

- IDE:

My advice: if you feel like it, learn either vi or emacs. I haven't seen anyone use a higher level IDE (including me, I use Webstorm, used to use Idea) as productively as vi/emacs users do. Also, vi/emacs users love their tool with passion. That says something about these pieces of software..
When I was working with c++, emacs was awesome and eclipse wouldn't even load the project. Then I learned to be lazy and use the mouse with IntelliJ. It's ok but their vision of what an IDE should be is getting further and further from what I think it should be (ie, don't try to replace the command line). However now I got even too lazy to go back to emacs..

And you know what ? The 1990's called and want their eclipse IDE back. I hope someone with an objective view can contradict me but eclipse is what a dell is to a mac. It's good, some people use it but it feels it's been developed with no real strategic vision of what an IDE should be. Lastlym keep an eye on online IDEs. A friend thinks it's the future. I'm not so sure but he is smarter than I am... Same for Light Table, keep an eye on it or even start using it. The guys behind it seems to have an unusual vision and smart enough for it to be really worthy of our time.

Now I realise I may have overstepped the answer to the question so I'll stop here :)

Cheers !

edit: paragraphs & indentation for readability