For day to day use I tend to use Firefox, and that's my default browser. That's more through "habit" than anything else and I frequently get frustrated by the amount of RAM its using etc.
Occasionally I'll fire up Chrome or Opera, and one day I'll probably switch allegiances.
In the meantime, what annoys me is that if I have (say) Chrome open and click on a link elsewhere (eg in an email) it'll open Firefox because that's my default browser.
I'm sure it would be possible to write a script that checks to see if any browser is open, and sends the request there, only actually starting the default (Firefox) if no browsers are open.
[Actually I think this ought to be the default behaviour for a range of apps; if I have a media player open don't open a different one if I double-click a media file, etc.]
Any suggestions for where I should start?