Well part of IE’s launching speed is hidden by the fact it is part of the OS thus some of its launching comes during system boot. 
If you want real launching speed go for Opera or Chrome, both are wicked fast on launch.
Personally I almost never close my borwser nor reboot my computer so launching speed isn’t a concern for me. What I care about is rendering speed.
On windows I found that Opera and Chrome load the fastest, by far. Firefox always seemed a bloat for me.
Then I started using Linux, and that basically flipped around. Firefox was faster and lighter than Opera - whereas Chrome wasn’t even available on Linux.
Now Chrome is available on Linux and it is by far the fastest browser available, in my experience anyway.
Simple way to end this discussion… no browser (or producer) is perfect.
Internet Explorer - Bad past, extensive testing required, lack of support for modern standards (beyond the usual), Windows only, closed source.
Firefox - Memory leaks (not the slowest but it’s dreadful for me), slowdown in turnaround speeds (in comparison to others), too many flavours (IMO).
Safari - Bloated, slow, ugly, become to chrome what Seamonkey is to Firefox.
Chrome - No proper RSS Support, Very limited functionality, Dependant on Google.
Opera - Dismissive of bug reports (seriously), closed source, poor marketing.
Let’s not forget that the IE development team is taking notice of web standards and introducing new technologies into the browser. Granted the speed of change is not ideal for everyone but they are in an unusual position of having to cater for many different interest groups (both internal and external) and billions of customers around the world.
Sure a lot of the issues are down to their own past history and mistakes but that’s the way it is unfortunately. IE8 gave us huge improvements and by the look of it, IE9 will be even better.
Anyone who’s a serious web developer knows that most of their time is spend futzing with their site trying to get it functional in any version of IE. Most other browsers…the page usually renders with few problems–and those problems are usually quick fixes.
Opera, Firefox, chrome, and even the current version of safari do a decent job at presenting a standards-based site as it was indented.
Now, as for myself…I’ve been an opera user for many years. It’s fast, highly customizable, and one of the most innovative. Most of the good ideas other browsers feature started out in the little-known opera browser.
However, version 10 has been full of bugs and issues that haven’t been addressed. One of the biggest complaints is that pages don’t fully load or load at all.
Firefox, yes, the memory leak issue is quite annoying. But, it’s quick, standards compliant, and has a large library of add-ons.
Chrome…it’s quick, but customizations are/were limited, and it is still being percieved as the “big brother” browser.
Safari…never used it much myself, other than just for website testing.