The 1898-O Half Dollar is a semi-scarce date that has often been perceived as being underrated. However, before comparing it with the dates that David Akers cited, it's important to point out that the 1898-O is a tremendous rarity with a full strike. Many examples, including those with the highest numerical grades are poorly struck, with weakness most noticeable at the upper right shield point (and adjacent wings) and on Liberty's lips. There are a couple of special examples that come tantalizngly close to being fully struck, but an example with both full lips and a full shield may not exist.
Comparing the 1898-O to the following dates -- 1896-O, 1896-S, 1897-O, 1897-S -- yields some interesting results, based on the PCGS Population Report. The 1896-O is the true star of the group. It has the lowest Mint State population by far (less than half that of the 1898-O). The 1896-S, 1897-O, and 1898-O have similar populations, with the 1897-O being slightly scarcer. The 1897-S has a significantly larger Mint State populations than all the others of the group. When examining the dates in this group for condition-rarity (how rare are they in high grade), the 1898-O and the 1896-S are the most difficult to locate above MS65.