well, I was using defaults, but mostly because I also use Sublime text 3.

But now my current setup is:

Packages

• minimap: Displays a minimap
• minimap-git-diff: Displays git diff within the minimap
• emmet: Emmet expands abbreviations for HTML, CSS, Sass/SCSS and LESS
• Omnisharp-atom: Allow for C# development in Atom

Omnisharp dependencies

• Advanced-new-file: Create multiple files and directories by typing a relative path
• json-schema: Json Schema enhancements
• atom-yeoman: Code generator to an initial c# file
• linter: Used by Omnisharp to visualize errors and other kind-of messages

Themes

• atom-material-ui: Material theme, without distractions.
• atom-dark: pre-installed syntax.

I have a very similar setup in Sublime text 3

I am using:

• regex-tester: Test Javascript regular expressions.
• sublime-style-column-selection: Allow column selection.
• copy-path: Copy file paths in many different styles.
• autocomplete-php: Autocomple to PHP. It's a provider to autocomplete+.
• language-smarty: Adds Smarty syntax highlighting and snippets to .tpl files.