What is the best OS for an old model laptop?

What is the best OS for an old model laptop?

First off, all Operating systems, regardless of the version, uses RAM in order to process all the applications that are meant to run. The primary difference that would be significantly visible would be the startup and shutdown times, as Windows 8 would generally boot up faster than Windows 7 or Windows XP. The same holds true for the shutdown time, as once again, Windows 8 would be able to shut down much faster than a Windows 7. However, since you are using a laptop that does not have touch screen functionality, the processes that you grew accustomed with using older versions of Windows (7&XP) would prove to be quite a task in Windows 8. This is because the interface of Windows 8 was designed for mobile devices like tablets and mobile phones, wherein the "Right-Click" is nowhere to be seen. 

Although there is an option to "Hide" the new interface and go with the classic desktop, most of the applications that you know where to find before, is no longer in the same location, making it difficult to adjust to the new environment. As of this time, it would still be best to stick to Windows XP. The Windows XP Service Pack 2 appears to be the most stable among the three iterations of Windows XP. Also, Windows XP has the most number of programs and applications supported. The program that you mentioned which does not run on XP should still be able to run, and you just have to run it in "Compatibility Mode" to ensure that it would still run. Windows 7, on the other hand, can run like a dream even on an older laptop. But, it is worth noting that to achieve that, most, if not all Windows Updates and background processes should be disabled whenever possible. 

Since Windows 7 has a lot of unnecessary bundled applications that are pre-installed, it would be best to reinstall the said OS with these unnecessary applications un-ticked and/or declined upon install. In addition, Windows 7 can be tweaked to run under minimal processing power and RAM. Some of which are pretty basic, like changing the skin to "Classic Windows XP" and choosing "Best Performance" over "Best Graphics" in the interface menu. As for Windows 8, it is the least viable option to go with if you are using that laptop. 

New applications should not be a problem with Windows 8, but the overall user experience would be greatly affected, especially for users that have been using other versions of Windows since the beginning. In summary, with all the factors considered, Windows XP still proves to be the best option, while the Windows 8 comes in second, and the Windows 7 goes last.