I think it depends on what you are trying to achieve ...
a lot of retro p+c pixel games tend to be made using AGS & there is as mentioned loads of help on the community as well as plenty of free games, demos & so on for download but it does lack support for high resolutions seeing as it only goes up to 1024x768 (I think)
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As for me I chose Visionaire Studio because it works in a similar way to VB (visual basic) - a lot of the game design process can be done visually & by selecting actions & options via dropdown menus, tabs & pop-up boxes as opposed to having to write loads of code.
I wanted full HD support!
various set resolutions from 320x200 to 1920x1200 or you can set a custom value in the explorer tool. (standard HD res is 1920x1080)
Also as far I'm aware there is a working mac port intended for the next release as well as loads of other nice new features - some to do with audio side of things.
Plans are also made for multi-platform support in future releases - iOS, Android etc but they don't know how long until they get implemented.
Also there is now a lot more support on the community as well as project starter templates, some video & text tutorials & finally some LUA Script examples.
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I haven't tried wintermute so can't say much about it.
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there is also another engine I know of but haven't tried called "SLUDGE - Adventure Game Engine" - which is also free open source.
http://opensludge.sourceforge.net
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Safe :)