I think the right choice is to quantify or bound what you mean. "The chance of X is 52%" sounds pretty confident and assertive. If you can't be that precise, th

I think the right choice is to quantify or bound what you mean. "The chance of X is 52%" sounds pretty confident and assertive. If you can't be that precise, then "For reasons X, Y, and Z this is likely, though not certain." I think "probably" is completely fine though.