Turok I can't answer your question precisely, it all depends on your use and what you plan to do. I opted for 8 GB of RAM because I have a very standard use of my device, I don't play games or do heavy tasks.
Having perfectly optimized software with no frills greatly reduces the need for RAM, and browsing is perfectly fluid, whereas other mainstream Android devices boast about their hardware performance in their marketing to try and disguise terrible software quality.
If you think 8 GB won't be enough for you, go for 12 GB.