The MSR Whisperlite makes no sense. It cannot simmer. You have little flame control. (Yeah, I realize that one can put less pressure in the tank and thus lower the fuel output, but hey, who wants to futz? Not me.) For what it does (or really, does not), it weighs a ton. According to MSR, it's minimum weight is 11 oz, whereas its International counterpart (designed to burn more fuels) comes in at a scant 0.5 oz more.
So what gives? Why is this the most popular white-gas stove of all time? I'm not sure. I need some research here. I believe it was the first stove with a remote burner.
Maybe it is the marketing approach to the stoves. The Whisp is billed as "Fast and Light" where as the Internationale is billed as "expedition." With regards to fast and light, ula-equipment.com has a brilliant rant about how "fast and light" is stupid. It's about steady efficiency. You're not traveling any faster, but you are traveling more efficiently. And you're doing it at a constant pace.
As far as the Internationale goes, the XGK tops it in everything it can do. Again there is a weight issue, but anything the Internationale can do the XGK can do better. The XGK is more stable, also, than the Internationale. The XGK also has the reputation as the classic blowtorch snow-melter.
Why is the Dragonfly billed as "gourmet?" Probably because it can simmer, not because it's insane snow melting abilities or cooking capabilities.
So why is these stoves still on the market? Demand, probably. If ain't broke, don't fix it.
MSR makes a large variety of stoves. However, If I had to pick one stove to cover everything, I would buy a DragonFly, as I did. Why? Why is it so much better than the venerable Whisp? The answer is simple: Flame control and pot support. I can do almost anything with the DragonFly. I can simmer, saute, do shore lunch, melt snow, boil massive quantities of water. The only area it lacks is multi-fuel capacity.
In addition, the Dragonfly has extremely wide pot supports. The six pot contacts guarantee that there is at least three points of contact with the pot, and it guarantees those points are on the same flat plane.
It all boils (s'cuz the pun) down to a simple, simple thing: MSR needs to make a multifuel version of the DragonFly. Thus, one stove could perform all of the function of four current white-gas stoves stoves (DragonFly, XGK-EX, Whisp and Internationale).
I have not used the Simmerlite, but have heard of its use in similar conditions to mine. I will say this: it is your lightweight white-gas stove. If you know what this is what you need, then go for it. It fills a portion of your system (see below).
And this is only for their white-gas stoves. MSR has multiple canister stoves: PocketRocket, SuperFly, Reactor and Windpro.
I have the PocketRocket: slight bias there. Each of these fill their markets, though. The PR is your ultralight solution. The SuperFly is designed to be used as a hanging stove. The Reactor is an alpine snow-melter (and if I had a use for it, I would pick it up fast!). The WindPro is just there. No need for it. Anything it can do, the others can do better. It's only claim is that it has a wide flame, but a good cook can deal with this (If only MSR designed the PR like the SnowPeak Giga Power and gave it a wide flame, perfection!)
I see a person's outdoor equipment (lovingly referred to as gear) as a system. Everything should work with everything else, and you should be able to cover all reasonable temperatures (Temps for me, being 100 F to -30 F). Naturally, as your individual specialites grow and your temperature range increases, your gear closet expands. For example I have three stoves, two (soon to be three) sleeping bags, three tents and two ground pads. And there still a lot of stuff I'd like to add to that collection.
Gear that does not fit this system should not be in it.
Looking back at stoves. Unless you need a stove for a specialized setup, I think one needs at least two stoves, maybe three. Here's what they are:
1. Winter stove: White-gas stove, capable of high heat output to melt large quantities of stove. Should have a fuel capacity for multi-day trips where running out of fuel could mean disaster (or cooking over a fire). This stove should also be able to be used for car-camping - i.e. you need to be able to simmer.
2. 3 season stove - This is your summer-weight stove. It should simmer to cook things delicately if need be, but it needs to be able to hit a hard boil. It should be lightweight. It needs to be able to cook for 2-3 people. The Fuel choice does not matter so much, but white-gas stoves will weigh more.
3. (optional) Solo stove - For many people this will be your three season stove (and probably a canister one at that). However, for the crazies out there, there are alcohol stoves of their endless derivations. These needs to be able to fit your cooking needs, and if you're cutting weight to the point of going with an alcohol stove, you've probably already cut your food weight down to dehydrated everything. Enter the Alcohol stove, which can boil and not do much more.
To fill the above slots, I have the DragonFly, the PocketRocket and a Gram Weenie Pro. I think they meet all of my needs. If I had to get one more, It would be either the XGK or the Reactor (alas, I do not have a use for either).
The Whisperlite does not fit into the above categories. First, it is not ultralight, so it is not in the third categoriy of alcohol stoves. Second, it is to heavy to be a three-season stove. 11 oz plus the bottle is too much. It also lacks simmering ability. Third, and finally, I would rather not use it in winter because there are better stoves, such as the DragonFly and the XGK.
So MSR, build me a better stove - get me a DragonFly that can run on the XGK's fuels.