When two boats share the same hull type — in this case both the Sundance NX17 2012 and the Sundance NX21 2010 are modified vee designs with fiberglass construction — the buying decision usually comes down to a handful of practical questions: how many people are you putting on the water, how far do you trailer, and what does your tow vehicle weigh?
Size is the most obvious dividing line here. The Sundance NX21 2010 measures 21,1 feet overall (2010), giving it roughly 3,9 additional feet of deck space compared to the Sundance NX17 2012 at 17,2 feet (2012). At 135 lbs and 185 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 115 hp, the Sundance NX21 2010 has a 25-hp advantage over the Sundance NX17 2012's 90-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Sundance NX21 2010 carries 45 gallons versus 29 gallons in the Sundance NX17 2012. 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 Sundance NX21 2010 is rated for 8 passengers, while the Sundance NX17 2012 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sundance NX21 2010 could be the deciding factor.
Bottom line: Choose the Sundance NX21 2010 if your priority is putting more people on the water — it handles 8 passengers and at 21,1 ft it has the deck room to back that rating up comfortably. The Sundance NX17 2012 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.