The Marathon Jon - DN 1436 2009 is a flat-bottom design and the Marathon Seneca 12 2010 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 Jon - DN 1436 2009 at 14,0 ft versus Marathon Seneca 12 2010 at 11,7 ft. At 130 lbs and 121 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 - 15 hp for the Marathon Jon - DN 1436 2009 and 10 hp for the Marathon Seneca 12 2010. 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.
Both boats are rated for 3 passengers - a good fit for a family of four or five plus guests. Comfort at capacity is another matter; the longer hull typically means more seat options and better weight distribution.
At this size, power-to-weight ratio matters more than outright horsepower. The Marathon Jon - DN 1436 2009 comes in at 9 lbs per hp versus 12 lbs per hp for the Marathon Seneca 12 2010. 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: The Marathon Jon - DN 1436 2009 at 14,0 ft is the right call if deck space, comfort, and entertaining are top of your list. The Marathon Seneca 12 2010 at 11,7 ft wins on trailering ease, likely lower purchase price, and simpler docking - a solid choice for a buyer who wants more boat for less money.