I would go with 200, and it looks like what the devs were going for as well, but it highly depends on role/agent/playstyle. If you are a jett, generally 250 or so, but if something like a breach, more like 170
It tends to be about 195 for the major events. i.e. Masters Berlin had about 196 for the event. It can vary a bit though. There was a little spike in ACS due to the fact that Riot started counting non-damaging assists as 25 ACS, and a lot of newer characters get a lot more assists.