I have a MacBook Pro (15-inch, Late 2008) and am currently running Snow Leopard 10.6.8. I would like to know which is the most stable upgrade for my model. I have read some reviews of Maverick and Yosemite making the older macs slower. Is this true?

I have a MacBook Pro (15-inch, Late 2008), Intel Core 2 Duo 2.53 GHz, 4GB Memory. and am currently running Snow Leopard 10.6.8.

I would like to know which is the most stable upgrade for my model? Mountain Lion, Mavericks or Yosemite?

When I had gone to the apple care centre in India a few months ago to upgrade my OSX to Mountain Lion, I was told that considering my macbook pro's specs, upgrading it would just make it less efficient, and that I should stick to Snow Leopard unless I consider buying a newer mac that would benefit from it. Is this true? I find it a bit hard to believe. Which update is most recommended?

I also notice that my mac has gotten considerably slower. While using chrome, it buffers and struggles with even just 5 tabs open. Could this have something to do with my current ios? As a precaution, I have always been making sure I have enough free space on disk i.e around 70 - 100 free out of 250GB.

Any advice is appreciated.

Thanks in advance.