Both are equally good with distinct features. However, if you are new to computerization and software access, I suggest WINDOWS 7.
If you like learning and exploring the modern computer with the newest implantations of technology, and are an adaptable learner, then WINDOWS 8 is for you! As it is the closest step towards modernised features.
However, WINDOWS 10 is already in the market now. If you are interested, then you can try this latest version as well.
Hope it helps :)
Let me know if you have any more queries.