An 8 plus. I first upgraded an El Capitan beta on my old 17" Macbook Pro i7 with only 4 gb of ram. All seemed well until I tried to open Vivaldi (chrome based browser). I basically did a hard reboot and tried the rest of the system. No problems with Firefox or Safari. I typically use Airmail 3 and that was fine. VLC, etc. no issues. I then did a wipe and fresh install but the results were the same. Running Dropbox, Firefox, Activity Monitor, VLC and Airmail 3 only brought me to 3 gigs of ram use. CPU was very stable after indexing etc. was complete. Still no Chrome, though.
Then I did an upgrade on my late 2012 i5 Mac Mini with 10 gigs of ram. This is a daily use machine and I went from El Capitan latest beta to Sierra with no problems. At this time I'm using 3.6 gigs of ram with Firefox (47.0), Airmail 3, Dropbox, Activity Monitor running. Very stable and all my usual apps open & run with no problems. I'm staying away from Chrome until Google addresses the ram usage from their end. Opening Vivaldi pushed everything up to 8.6 gigs with only 1 tab. I haven't used Apple's Mail in a long time. I've found it to be a bit glitchy sometimes on my machine and Airmail has always been very stable & light on resources.