Which IDE or text editor would you use to professionally write CSS and HTML?

I think it's just a personal preference. Coda, Sublime Text are solid. As for something a little different but still solid, I'd say check out Atom its a solid text editor. Solid open source packages, themes, ect. They are all pretty much the same just little differences.

I'm personally fond of Coda, which is designed with languages used to code for the web in mind. Note that Coda is an OS X program only.

I know lots of people like Sublime Text as well, but I don't have any personal experience with it. I have heard only good things though. You can use Sublime Text on OS X, Windows, and Ubuntu.

So I would recommend checking out one of those. :)

Sublime Text 3

I use Sublime Text 3 for the majority of my front-end development needs. Packages I use include a color highlighter for CSS colors codes, Emmet (a must have) which gives me a fast way to create things by doing this ul>li*5, HTMLPrettify, and numerous Linters/language completers/auto-suggestions.

Sublime 3, Atom, or Cloud9

Just depends on my mood.

Thank you all for your excellent input! I really appreciate it!