I'm a fan of Smultron as well. I've been using it for a few years. I don't maintain a large, complicated code base so I haven't felt anything lacking. The editor itself is nice, it handles multiple files and interacts with Finder pretty well and the syntax coloring works well. I created a syntax definition myself which was also easy.

I also like the easy shortcuts for moving text blocks, commenting, chopping, conversion, etc. I'd say try it out, then buy TextMate if you don't get what you need from Smultron.