The Wolf has a dual stacked burner which should give you an excellent simmer. Thermador (unless things have changed recently) achieve a low simmer by cycling the burner on and off with the ignitor constantly clicking - some people find this annoying.

What are the problems with the Wolf simmer - I've never heard of any.

The clickety-clack on Thermador happens on super low simmer setting or 100 degrees F. Wolf can't achieve this low a temperature, neither can most gas burners.

At 130 degrees,a standard low simmer,Thermador does not make noise.

Thermador heat will be more even due to star burners.

I would get Wolf Oven and Thermador cooktop if those are the two brands you are considering.

I just moved to a new home with a Wolf cooktop. Previously I have owned a Thermador cooktop for 14 yrs and more recently a Thermador range for 12 years with the clickety simmer. I love the Wolf. I never have rice boil over like I always did with the Thermador. The simmer is a true simmer for me. I am extremely happy with it. I also got the Wolf conv/micro and wall oven, and once you figure out how to use them, they're great.

In order to evaluate how low or how high burners go you need to know how many BTUs the burner will deliver at either end. The actual temperature of your food is then determined by the cookware and what you are cooking. A temperature rating given for a burner is an extrapolated number of no meaning. On the low end, Thermador is 375 BTUs on two burners, and Wolf lists theirs as 325 BTUs on their simmer burner. I am betting the difference is negligible, but only you can say if the clicking would bother you. I have Wolf and love it. I get a great simmer on all the burners. The other burners are higher on the low end, but because you use a bigger, heat conductive pan, the actual temperature of the food stays low. If I use cast iron on the same lowest simmer, it will hold on to the heat and the temperature is higher.

When determining how even a burner heats, the star shaped burner may produce a more even heat if you are using a thin cheap pans or to some extent one that is poorly heat conductive, like cast iron, steel or stainless steel. I mostly use a 12 inch skillet that is an old "Piqua favorite"(brand) and a couple of deBuyer steel pans that are pretty even with my Wolf burners. I have a couple of cast iron pans that aren't as even. Most people however, do not use thin cheap pans on these ranges. The exception might be specialty cookware like a paella pan. We have a big one that would not heat evenly on any range burner because it is so big but we use the outdoor grill to cook with it.
The biggest factor in producing even heat is your cookware. Copper and aluminum in adequate thicknesses are the best heat conductors in commonly found cookware. This is a very informative article that explains the importance and types of cookware.

Here is a link that might be useful: Understanding Cookware

I am confused despite more than 30 years cooking. I was so excited to get my new Wolf gas cooktop because of the simmer facility. I always thought that simmering meant an occasional bubble. With my cooktop even the high simmer has nary a bubble to be seen. Where do I go to learn about simmering if the cooktop is right and I'm wrong?