I'm not going to knock Dell because they have been good to me. Dell was the first PC I ever purchased as a Computer Science student and I have been loyal to that brand. I started off with a used desktop and when there were problems, the company did it's best to resolve it. Of course, I raised hell but in the end it worked out.
Case in point: this laptop I'm using now. I received this in 2010 as a replacement to a laptop I purchased in 2008. So for about $1600 or so, I've had a good laptop for 5 years.
The problem many people have is thinking all products in the same brand will perform the same. My sister purchases a $600 Dell and wonders why it's slow - I tell her it does not need more RAM, it needs a dustbin.
Anyway, if you want something that will last and work well for you, buy the best machine you can afford. We all know there are 2 basic things - memory and processor. Another is the brand - some brands are better than others, so do your research and choose wisely.
Also, whether you run Windows or OSX, it doesn't always make or break your experience. Most of the issues are related to user error. Installing junk apps, spy-ware & bloatware; running without anti-virus programs or outdated programs, or expecting a $500 machine to perform like a $2,000 system.
OSX or Windows - buy what suits your needs. Windows is not that bad.