I sincerely apologize that this will (and does) read like a long comment, but the comments section is too limiting to make the point.
The odds are that the only person who could answer this question well would be an active bearer of the priesthood in one church who apostatizes from it, converts to the other and thereby becomes an active bearer of the priesthood in the other.
...and that might be a pretty small group of people. Active members of any church rarely convert to other churches.1
Let me cite a few examples of the problem.
(Pro-LDS) The Encyclopedia of Mormonism in the article "Catholicism and Mormonism," under the subheading "AUTHORITY," gives a bland one-paragraph statement that basically only introduces the idea of how the two organizations look at the authority held by the apostle Peter. (And, IMHO, it doesn't even do that particularly well.)
(Neutral) In "Mormonism: An analysis of doctrine in comparison to Catholic and other Protestant faiths"2 author Anne Latham of the Massachusetts Institute of Technology tries to describe the LDS perspective in comparison to other beliefs. The article compares very few things, and it's obvious that she either isn't LDS herself or is writing from a non-LDS perspective. For example, she explains that men receive the Melchizedek Priesthood when they become High Priests. Actually, men receive the Melchizedek Priesthood when they are first called to serve in any M.P. office, most commonly the office of Elder after they turn 18 and prepare to serve a mission.
(Pro-Catholic) A third example comes from Catholic.com. The article is a decidedly anti-LDS article filled with shallow statements that misrepresent the LDS faith. Which is curious, as this apparently not-affiliated-with-the-Catholic-Church ministry claims it began when "a Fundamentalist church in San Diego, California, decided to leaflet the cars at a local parish during Mass. The fliers attacked the Eucharist and were riddled with misinformation." (source).
My point is, neither organization really understands the other.3 I would hope there are scholars in each that could answer this question with the objectivity it needs, but if there are, they're not publishing on the Internet in a way that's easy to find.
Recommendation
Therefore, I recommend this question be deleted. Instead, I recommend you ask something like: "From the perspective of [sect], how is its priesthood or ecclesiastical authority derived, organized and used?" This will get you detailed answers about specific priesthood practices that can thereafter be compared. And I suspect the group of people who can answer said question(s) increases thousands fold.
1 This is perhaps an egregious blanket statement. Let's put it another way, "people who are so active in their church that they participate in leadership and/or ministerial roles rarely convert to other churches." And whey they do, it's usually after a crisis of faith that led them to wonder why on earth they're attending the church they do.
2 Frankly, the title of this article and its hosting school should have foreshadowed its quality. I'm hoping the author left the word "other" in as a typographic mistake and didn't really mean to imply that the Catholic Church was Protestant. Or, perhaps, she mistakenly left the word "Protestant" in and meant Catholicism and other churches? And why am I reading a religious article from an institute of technology? Anyway...
3 Which isn't surprising. In fact, speaking about each organization's membership generally, it's probably fostered and desirable. But, perhaps on a more positive note, speaking from my own perspective as an active LDS member, my religion is my life. There isn't a whole lot of time available to really study other religions. That's why sites like this are so valuable.
