MacOS – Alternative for Notepad++

Have you considered Xcode?

I know you said you don't like TextMate, but it's one that meet pretty much all your needs.

which is fast

TextMate
Really fast

Xcode
Not that fast but not Eclipse/Netbeans-slow

which does syntax highlighting

TextMate
Very complete and extensible

Xcode
Does syntax highlighting, it depends on your needs

were I can define own syntaxes (or there are many plugins e.g. for YAML),

TextMate
Very, very extensible

Xcode
Syntax extensions are possible

where the developers are active,

TextMate
Some say it's vaporware, yet very few other text editor can compete with its current features

Xcode
Apple development of this program is very active

which does not have the look & feeling of TextWrangler

TextMate
If you don't like the sliding bar, there's a plugin to replace it by a drawer

Xcode
Doesn't have a sliding bar

which can define projects (like Coda can)

TextMate / Xcode
Do projects

which includes a basic support for Git and/or SVN

TextMate
Support for Git/SVN/Mercurial (and probaby more) via built-in and added plugins

Xcode
SVN support for 3.x, added Git in Xcode 4

which supports a fast autocompletion

TextMate
Basic variable/function completion
very complete code completion via bundles

Xcode
Basic variable/function completion

MacOS X 10.6 compatible

TextMate
Some compatibility issue

Xcode
Fully compatible

I have about 7 years of experience coding in a Windows environment before I got my first mac early this year. So I know exactly what you're talking about. I was very used to the combination of Visual Studio for c++ and .net, Notepad++ for .bat and other scripting and lightweight tasks, and the occasional bit of Eclipse for java.

When I first started using my Mac, I was frustrated by what I saw to be a lack of equivalent software for OS X. I tried different IDEs and text editing solutions (Eclipse, Aptana, Textmate, Smultron, Fraise, etc), but like you said, nothing really 'clicked'.

However, at some point I stopped looking for replacements and started using the tools that were commonly used on *nix machines. Particularly vim. I've found that once my expectation of finding software equivalents to everything I had used on Windows dropped away, my horizons broadened. I feel like my interest in coding has been renewed because I'm learning a completely different way to work and think about the process. I'm using the command line way more than I ever have in the past, and this has translated into new techniques even in my Windows development (like using powershell and command line versions of tools rather than the gui).

I was in a huge programming rut before I started using my mac, but I'm finding that being forced to look at my process and tools in a different way is really bringing out talents and interests I didn't know I had before. I'm coding in python and c++ rather than javascript and c#, in one of the oldest editors in existence, and I'm loving it.