I agree, use the HTML5 DOCTYPE:
It's short, easy to remember, and backwards compatible with HTML 4.01.
If your question is strict vs. transitional HTML 4.01, I'd go with strict. Transitional allows you to use presentational elements/attributes that have been deprecated, which allows for sloppy coding habits that will ultimately only make your job harder. If you're writing strict documents, then use the strict doctype. It's really only used for validation purposes, so using a transitional doctype may give you a false sense that you've written only strict markup.