Depends on what game you're playing. Quite a few games now have 8 gig has a MINIMUM, with 16 gig recommended. So since you're already on an 1151 platform, honestly I would start with ram. Another 8 gig will provide for a solid foundation for today and the next few years.
However, if you play a lot of older games and don't think you will see a benefit from 16 gig of ram right now, save that for later and upgrade the CPU. The i3 is ok on a pauper's budget, but you get a lot more bang for the buck with the i5's. Microcenter currently has the i5 9600k for $230 on sale. It's a Gen 9 cpu, so you'll have to be running a Z390 chipset (or Z370 with bios update). Once you eliminate the i3 as a bottleneck, imo you'll get a lot more out of your future video card upgrade.