Its a matter of taste.
I currently use Komodo Edit. That is partly because it is very good, partly because I also use it for coding, and partly because it has very good support for Django templates. It can spot syntax errors in HTML and in many languages. It is cross platform. It is reasonable at editing files on remote servers.
vim and gvim are flexible, light and fast, but the learning curve is steep. Macvim if you are on a Mac, Gvim otherwise. Some people live it, some people hate it. Its worth having some familiarity because the console version is available in every Unix type OS so can be useful in emergencies if you have sites hosted on Unix or Linux.
Bluefish is also cross platform, but was never to my taste.
On Linux I like Kate. Together with Konqueror it is the best way of managing and editing files on a remote file system.
Gedit is mostly used on Linux, but is cross-platform.
All of the above are open source, and a number of others are freeware. Look through the forum for other options (especially Mac and Windows ones, because I cannot recommend them myself). Most of them have their advantages: try them out an pick what works for you.
I have gone from Quanta Plus, to Kate, to Komodo Edit, so keep your mind open to trying new editors as your needs change. Some people will disagree with that as they prefer to learn one editor really well, but I use different editors for different purposes (Komodo Edit for code and HTML templates, gvim for HTML marked up content and quick edits)