Stihl vs Husqvarna is to loggers as Ford vs Chevy is to racers. Talk to 10 random loggers and you will find about a 50/50 split between those who prefer Stihl chainsaws and those who prefer Husqvarna chainsaws. Everyone has their own preference and reasons why the use the chainsaw they use. Both brands have high quality professional grade models that preform well in the woods.
Your Personal Preference
It really boils down to your cutting style and preferences. Loggers who like a Husky say it will speed through a cut faster so they can make that final cut on a tree as it falls quicker, thus giving them more time to get out of the way. Stihl enthusiasts will say they like their preferred chainsaw because it has the low end torque needed to power through the toughest pieces of wood with ease.
The fact is that both companies make great saws. I would recommend trying models from both brands of comparable size and power to see which one you prefer. There is an easy and fairly cheap way to do this. A lot of equipment rental companies rent out Stihl and Husqvarna chainsaws by the hour or day. You might not find the particular model you are looking for but you can get a feel for the brand by testing a saw of the same brand that comes close. Be sure to ask how many hours are on each saw and how old they are. If you run one chainsaw that is significantly older than the other one you will get skewed results. It would be a good idea to run each saw for a full day to get an idea of its features and benefits to you.
After you have run each chainsaw for a full day, write down a list of things that you liked and disliked about that saw. When you take the saw back to the rental store ask the mechanic if that saw has had a need for more than average maintenance. Has he had to service the saw frequently and has it taken many hours of use and abuse? Which brand of chainsaw does he prefer? and Why? Ask other loggers or arborists that you know what brand of chain saw they prefer and why. Compare your notes and buy the brand of chainsaw that your prefer.
My Personal Preference
Which brand of chainsaw do I prefer you ask? Well, I like Stihl over Husqvarna. I have run both brands and I just prefer the torque and ease of maintenance of a Stihl. I have owned several Stihl chainsaws and one Husky. I have run and blown up two Husqvarna chainsaws, but to be fair both saws were more than two years old and had seen many hours of daily use and abuse. It was after that I bought a Stihl 066 chainsaw.
I started using my Stihl and doubled my production. I found that the higher rpm's that the Husqvarnas ran at, was hard on bars and chains. I was constantly tightening chains and many times the chain would stretch too much to use before it had worn down completely. You may find that this is not the case for you, a lot of times all is required is to find the right bar and chain combo that works best for that chainsaw. It may have even been that those Husqvarnas needed some repair on their bar oil distribution system. All in all both brands are of very high quality and I am confidant that you will be happy with either saw.