IE can't be deleted. However, it can be uninstalled.
Start > Control Panel > Add/Remove Programs
Click on the Add/Remove Windows Components at the left hand
side.
Uncheck Internet Explorer. Follow the on-screen instructions and
Internet Explorer will be removed. If you want it back, repeat the
above steps, but check the Internet Explorer box.
You can't compare which is better than which. Personally, I like
Firefox because I won't be affected by ActiveX. I can use Maxthon
or Avant if ActiveX is really needed or if the website can only be
viewed in IE and no other browsers. This happened to one of my web
hosts, when it completely revamped and is no longer compatible with
Firefox.
They won't slow down the computer, unless you run all of them at
the same time.
Maxthon is the only browser I know that can view every website that
IE can. Avant can do it, but not as well as Maxthon does.