I've had a MSR Whisperlite Internationale since 2001, It's a very nice stove that has been very reliable. Have run it mostly on unleaded petrol with a small amount of coleman fuel on occasion.
If you are careful, you can simmer on it, but it does take a fine touch to do so. Be aware that the heat output of the MSR multifuel stoves are intense, I melted through an ali cook set, delaminated a copper bottomed stainless set, and warped a cheap stainless set before admitting that I was going to have to fork out for a decent set of pans, in the end I got the
MSR Alpine Cookset to go with the stove. As a system it works very well, the stove fits inside the pot nicely.
Only downside I found with the whisperlite is that it doesn't burn diesel. As such I got a Dragonfly to go with it, useful in base camp for cooking bigger meals alongside the whisperlite, but also allows me to burn diesel when venturing further afield. Downside of the Dragonfly, it's LOUD, like cooking on the exhaust of a fighter jet. But you do have lots of control over the heat output, and it will burn pretty much any liquid fuel...
Thanks
J