If it were in a league, would it be bronze?
This is obviously subjective, but from my experience:
- Medium - Low Bronze ( I could beat this when I started, and I placed in bronze)
- Hard - High Bronze ( I could beat this regularly before I was placed out of bronze, possibly low silver?)
- Very Hard - High Silver? (I can beat this regularly, and I'm ranked now mid-gold).
Short answer: it's probably somewhere around bronze or silver.
However, more importantly, the AIs do not play according to the modern metagame. This means playing against a human opponent in bronze or silver will still seem vastly different from playing against any of the AIs.
More specifically, the AIs usually don't follow any sort of modern build order. For example, if you're used to playing against the AI, you might expect an attack at around the 10-minute mark with Roaches and Hydras, but versus a human a Roach bust might come much sooner and is much more deliberate.
It really depends on what strategy you play. The AI basically has only one good timing push, especially on "Very Hard". If you go for one base play it should be quite easy to stop the computer, create an expansion yourself and finally kill him.
Should you try to expand early the timing push is way harder to stop. Usually this involves you following a good build order and getting static defenses. The less defense you get the harder it gets, but you will have an advantage later on provided you survive.
My estimate is (provided you fast expand):
- Hard: Low Silver
- Very Hard: Low Gold
But if you fall for cheeses then it could look much worse, as real opponents do not follow the strict rules the AI has to obey.