I asked myself that exact same question a few years ago, and for better or worse, I decided to go with a free Wordpress blog. It is an exceedingly easy platform to work with, but the formatting options are quite limited unless you go for a paid subscription.
Instructables is a brilliant site, but it has such a dramatic range of traffic, and such a large number of tutorials it's really hard to know how many people would see your work. Some tutorials get nothing, while some go past 100K, and that probably depends on whether you are doing something that is currently a hot topic.
The only real data I can provide is from our project site:
More than 95% of that traffic is to the tutorial-style pages,
and the most popular is the
Arduino UNO Datalogger for Complete Beginners page
which had ~24 thousand page views in 2017
Older tutorials, like the one on the DS3231 RTC
and the one describing our work with the MS5803 pressure sensor
have settled down to a reasonably stable 10 thousand page views, per year, per post, and that seems to be the typical pattern.
By comparison, the Serial Plotter Tool with an UNO DAQ tutorial I put on Hackster.io only sees about 2500 views per year.
I participate regularly in several forums, but that produces very little referral traffic to the blog. > 90% of the traffic comes from direct Google searches, and ~6% of the overall traffic comes from Pinterest. I have put significant amounts of time into other platforms like The Cave Pearl Project | Hackaday.io and our content was copied out to other sites like wevolver, but the cumulative referral traffic from sites like that is essentially zero. Many of those content hosting sites are silos that successfully lock-in their viewers.
How much any of this applies to your work depends on whether your work is general, or niche. The loggers we work on are a tiny little corner of the larger Arduino ecosystem, and I suspect that tutorials on more popular topics like self balancing robots would get much more traffic.
Anyway, I hope that helps you with your decision!