Took my MacBook Pro into the shop today to have the battery replaced and had the operating system installed.... jury's still out on the system, gonna take some time to get used to!!
The versions 10.8 (Snow Leopard) and 10.9 (Maverick) in my eyes were the best ones during the last years. And they were "operating systems".
the new 10.10 is a lot more iPad / iPod friendly, too... but the girls here know more about that than I do ....
I like the actual version 10.10 (Yosemite) as well. The actual iOS 8.x versions from the iPhone and iPad are very well integrated, iPhone/iPad in my eyes work together with iMac/Book and so on very smoothly. But what I don't like at all, is the lookalike of Yosemite: they tried to make an operating system look like your iPhone - just ugly!
Sadly Apple systems are very pricey and have become less durable lately (maybe because it is based on Intel chips like the majority of PCs), so I prefer to use Linux based machines, which can be configured to closely act like a Mac with comparable security features but a better choice of (ususlly free) software.