Msr
Well, I'll comment here.
I've used the whisperlite for several years. Got a lot of use out of it, including over 1000 miles of AT. Before that, I used the Svea 123. I gave up on that after all the gaskets dried out and cracked, and had flames shooting out of everywhere!
With all the use that the whisperlite has had, I have never had it expode, or melt down. Perodically, it does clog up, probably because I'm using old fuel. When that happens, I take it apart and fiddle with the shaker jet. This year, I replaced the gaskets in the pump after one cracked. Other than that, I'll continue to use it when suitable.
Like others have posted, no need for the multi-fuel version in the USA. White gas is abundant. (I'll try unleaded gasoline on my next long bike tour).
Simmer? Can't really with the whisperlite. But, with things like Liptons where you boil for 10 minutes, it would be nice to be able to regulate the heat better.
Lighting and preheating problems? just crack the valve and get some gas into the priming cup and light. Not a long process.
That being said, I haven't used the Optimus or Dragonfly, so I can't comment one way or the other on them. But, before thru-hikers went to alcohol, the whisperlite was the most popular stove. Must be a good reason why.