I work in IT for a large company in the mining industry. We are Global, therefore have global standards.
I had previously used HP, but due to very poor support ethics and service, I gave them the flick.
The global beast has been using Dell for a number of years, and yes, they do have issues, but we have the Premier support, so we get them fixed NBD, the tech will either send out the parts, or a tech to do the installs.
Just stay away from their Alienware products.... any of the Latitude Laptops will give you good service, we currently run two different models, the E6430 and the M4700 which is a high performance machine, definitely not a lightweight machine for travellers.
Personally, I run, and highly recommend, a Macbook Air (with our corporate Windows environment virtualised) and a 27" iMac at home.
Depends what you want to run on the machine, standard Microsoft Office etc all runs on a Mac, but when you need something like AutoCAD or most of the business bookkeeping software, they don't usually do Mac versions..