I like the last best, as it seems usually the cumulative “I can do this at all without failure” or even the cumulative “I can succeed or even succeed well” odds are important.
Having read through the lengthy mechanics section in front of the rules, it seems in reading just a bit fiddly to me – lots of options, chances, factors, mitigators, consequences, etc. I suspect, though, much of that perception will disappear once we rolling and used to it and don’t have to think about it.