Both the Sundance NX21 2010 and the Sundance SV21 2013 are modified-V designs, both built in fibreglass, so 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?
On paper these two are close siblings in the size department - Sundance NX21 2010 at 21,1 ft versus Sundance SV21 2013 at 20,6 ft. At 1 850 lbs and 1 850 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 200 hp, the Sundance SV21 2013 has a 85-hp advantage over the Sundance NX21 2010's 115-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Both carry nearly identical fuel loads - 45 gal and 45 gal - so range won't be a tiebreaker here.
For family outings this is probably the sharpest distinction between the two. The Sundance NX21 2010 is rated for 8 passengers, while the Sundance SV21 2013 caps at 6. 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 SV21 2013 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 6 that costs less to run day-to-day.