Answer 1: Execution Ax beats Fullblade for most situations. Most people don't realize this, but as one of the people who ran the numbers when the Avenger was previewed, its true.
Answer 2: The difference is pretty negligible, so you probably shouldn't care.
Answer 3: But apparently you DO care, as evidenced by this thread. So if you try to take powers with high [W] values, go for the ax. If you go for powers with bonus damage or with effects other than damage, then hitting becomes slightly more valuable for those particular powers. Make a judgment call.
Answer 2: The difference is pretty negligible, so you probably shouldn't care.
Answer 3: But apparently you DO care, as evidenced by this thread. So if you try to take powers with high [W] values, go for the ax. If you go for powers with bonus damage or with effects other than damage, then hitting becomes slightly more valuable for those particular powers. Make a judgment call.