OS X hangs up intermittently - spinning beachball of death
I ended up taking the laptop to a Apple Store and they said that the hard drive bracket needed replacement. They agreed to do it for free since it is covered by the Apple Quality program. Apparently, the hard drive bracket is something that breaks in this model and Apple has the decency of repairing it for free despite being way out of warranty. One thing I will never know is why Windows performed well despite this hardware error. Anyway, my computer runs smoothly again, specially with the new SSD.