This is kind of like the "Where did you hear about Scirra?" thread, but I'm interested in seeing the software people have already discarded, which occasionally came up in that thread, and also why that particular solution wasn't right for you. (I've omitted things like Unity and UDK, which I wouldn't really use for the same kinds of projects)
In the past year or so I've tried Stencyl (formerly StencylWorks), Gamesalad, GameMaker and, of course, Construct to varying degrees to try and figure out which would be best for me going forward. These were my observations.
Gamesalad, I'll be honest, I didn't get very far with at all. I was on the Windows beta, but lost interest fairly quickly. I thought it would offer me some kind of magical solution for publishing to iOS without leaving Windows, Marmalade SDK style.
GameMaker is an interesting, relatively mature product and I've seen some nice things done with it, but I didn't want to learn a proprietary scripting language when there are other, more useful languages I'd like to learn. Overall, I also thought the editor felt clunky. I also had some performance concerns due to things told to me by wiser, more experienced GM users.
I actually still have Stencyl installed. I like the interface a lot, and I also like the way they're trying to implement their resource and community infrastructure within the application. In terms of ease of use and general accessibility, I think it's the closest thing I've found to Construct.
I think their UI for snapping code blocks is probably a great, visual way to teach programming principles to people who have never even nested an HTML tag before. That said, I don't like the emphasis on tile usage in game construction and C2's workflow is definitely more streamlined (note: not a euphemism for 'simplistic').
There are a few abstract reasons and many more tangible reasons behind my decision to go with C2. The core for me is that I think as the HTML5 platform matures, performance improves and support grows, Scirra customers are going to come out winners. That's why I got on board early.
How about you guys and girls?