The Contender 21 Open 2009 is a deep-V design and the Contender 31 Open 2007 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.
Size is the most obvious dividing line here. The Contender 31 Open 2007 measures 32,0 feet overall (2007), giving it roughly 10,8 additional feet of deck space compared to the Contender 21 Open 2009 at 21,3 feet (2009). At 3 550 lbs and 3 500 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.
The power gap is worth calling out. Rated to 500 hp, the Contender 31 Open 2007 has a 200-hp advantage over the Contender 21 Open 2009's 300-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Contender 31 Open 2007 carries 240 gallons versus 90 gallons in the Contender 21 Open 2009. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.
For family outings this is probably the sharpest distinction between the two. The Contender 31 Open 2007 is rated for 9 passengers, while the Contender 21 Open 2009 caps at 6. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Contender 31 Open 2007 could be the deciding factor.
Bottom line: Choose the Contender 31 Open 2007 if your priority is putting more people on the water - it handles 9 passengers and at 32,0 ft it has the deck room to back that rating up comfortably. The Contender 21 Open 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 6 that costs less to run day-to-day.