The Marathon Otisco 1236 2009 is a flat-bottom design and the Marathon Seneca Utility 14 2009 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 Otisco 1236 2009 at 12,0 ft versus Marathon Seneca Utility 14 2009 at 14,0 ft. Weight tells a clearer story for trailering families: the Marathon Seneca Utility 14 2009 tips the scales at 218 lbs - 108 lbs less than the Marathon Otisco 1236 2009 at 110 lbs. That difference is meaningful if you're working within a half-ton or three-quarter-ton truck's tow rating, especially once you factor in a motor, gear, and fuel.
The Marathon Seneca Utility 14 2009 tops out at 25 hp. Engine specs for the Marathon Otisco 1236 2009 aren't listed - confirm with a dealer before selecting an outboard.
For family outings this is probably the sharpest distinction between the two. The Marathon Seneca Utility 14 2009 is rated for 5 passengers, while the Marathon Otisco 1236 2009 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 14 2009 could be the deciding factor.
Bottom line: Choose the Marathon Seneca Utility 14 2009 if your priority is putting more people on the water - it handles 5 passengers and at 14,0 ft it has the deck room to back that rating up comfortably. The Marathon Otisco 1236 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 3 that costs less to run day-to-day.