Another +1 for buying a good quality Dell/Lenovo business class machine. If two motherboards have gone (even on cheap machines) you have either been very unlucky, or your doing something bad to them.
A big problem with lower grade PC’s is amount of junk installed when you buy them, which can cause problems and poor performance. With the business class machines, they come with less junk and sometimes a copy of the OS which allows the machine to be reinstalled cleanly.
I recently bought a new PC for use with my TV, and until all the junk was removed, it was unusable (that’s not overstating it). I don’t think you have problems like that with a Mac.
Although I can see some advantages with Apple, unless AppleCare covered 5 years, there is no way i’d consider one, they are just too expensive to risk having a brick after 3 years if something fails.