just wondering what people think because this seems kind of hard to judge sometimes. shahzam, boaster, ange1 come to mind for me
The issue is you're equating someone being educational as being a good IGL. You can be educational and be a mediocre IGL. As an IGL, your team all conveys information and an IGL decides what to do next based on information gathered. Hell, even Boaster/Shahz creating strats for each map and hero pool doesn't change the fact that that's not made during a game. That's great coaching, which is different.
I agree that it's hard to tell who is the best IGL, but the fact that Shahz has been around for a while and been highly successful, I'd have to give an educated guess and say he's the best IGL.
I choose shahzam because beside his basic quality as igl which already pretty good, he can control TenZ on what to do and what not to do.
He is the lone strategist and the one who review the enemy playstyle, watch old VOD, etc. And the coach too. Basically because SEN don't have analyst and coach so he do that too. That's what I think made him best igl.
2nd goes to boaster, because his strategy is so damn good. Watch some of his stream, when he analyze about post plant or line up or something with technical explanation is so great.