Mugen 1.1
I had my doubt about upgrading from 1.0 to 1.1, but after applying the 4gb "patch" the version es very stable and compatible.

Currently most of the chars in the archive are compatible with 1.1, unless the notes state the char is tied to an specific version, and yet es easier to find someone convert those chars to the 1.1. version. Converting chars from 1.1 to older version is harder because new version include new code options, replacing the those new codes with the old code makes the character bug or crash the engine.

I recently discover an old Mugen Windows char incompatible with Mugen 1.0 actually works in Mugen 1.1, funny enough the notes of such char never mentions someone editing the original char to make it work in Mugen 1.1

Also Mugen 1.1 fix a annoying bug with the stages where some elements show with a blackline in Mugen 1.0, this bug was very common. Also return the lost stage feature to scale down the characters so you can fight giant bosses ( this feature was loss in mugen 1.0)

I see many people complain the mugen crashes a lot, but in my personal experience, the crashes are caused due poor programed chars (mostly from edits from people who only know hoe edit the char, but lack the expertise to create a complete char). Im mostly using the releases from the original authors and my mugen is SUPER estable.