The Marathon DN 12 2013 is a deep-V design and the Marathon Seneca Utility 13 2008 is a modified-V design, so you're likely deciding between two noticeably different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
On paper these two are close siblings in the size department - Marathon DN 12 2013 at 11,7 ft versus Marathon Seneca Utility 13 2008 at 13,0 ft. At 121 lbs and 150 lbs respectively, both sit in a similar weight class - either should pair comfortably with most mid-size SUVs and half-ton trucks, though always confirm your specific tow rating with the motor added.
Both boats share a closely matched power ceiling - 10 hp for the Marathon DN 12 2013 and 15 hp for the Marathon Seneca Utility 13 2008. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup.
For family outings this is probably the sharpest distinction between the two. The Marathon Seneca Utility 13 2008 is rated for 4 passengers, while the Marathon DN 12 2013 caps at 3. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Marathon Seneca Utility 13 2008 could be the deciding factor.
At this size, power-to-weight ratio matters more than outright horsepower. The Marathon Seneca Utility 13 2008 comes in at 10 lbs per hp versus 12 lbs per hp for the Marathon DN 12 2013. The lower the ratio the more explosive the acceleration - meaningful on a short RIB where bursts of speed, quick planing, and agility in surf or tight waterways define the experience.
Bottom line: Choose the Marathon Seneca Utility 13 2008 if your priority is putting more people on the water - it handles 4 passengers and at 13,0 ft it has the deck room to back that rating up comfortably. The Marathon DN 12 2013 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 3 that costs less to run day-to-day.