It all depends on who you get. Writing patents is a one-person affair. It's hardly ever worthwhile for two or more writers to collaborate on a patent specification. The reason is, before number two can start to make a worthwhile contribution to the task, he has to spend hours getting up to speed on the invention -- who is going to pay for that?
Plus, if you go the large prestigious firm, you don't necessarily get the brightest and most experienced patent writer. You might get the least-experienced trainee. The trainee is of course "supervised" - but compare it with a trainee dentist, where the trainee practices (in your mouth) under very close supervision. The trainee patent writer is left more or less on their own. They really only learn because they are smart people (which they are), not because they are closely supervised by the experienced ones.
It is meaningless to measure the performance of the patent firm, as a whole firm. You can only judge the performance of the individual who is actually writing your patent. The supervisor does do a little more than check the trainees work for spelling mistakes -- but not much more.
The difference between a good patent and a bad patent is that the good patent protects all the variants of your invention that you are entitled to protect, and the bad patent misses some out. And that is a matter more of engineering than of law. Make sure your writer can focus on your true adversary, namely your competitor's chief engineer, not their legal department.
Seek someone to write your patent who knows nearly as much about your invention as you do, and is capable of quickly understanding the new thing you have thought of, and of tranlsating that new thing into words. That is the quality you want, not which firm they belong to, nor how successfully they handle big-budget litigation. (The people who handle the litigation don't write the patents, anyway.)
When seeking someone to write your patent, don't be swayed by the prestigious offices -- that just affects the dollars you pay. Seek someone who makes you feel comfortable that they understand your invention, technically.
Of course, I am talking about an invention from which you hope to make money. If you just want to be able to tell your grandchildren you patented an invention, anyone will do.