Both the Sundance DX18 2012 and the Sundance SV186 2011 are modified-V designs, the first built in composite and the second 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 DX18 2012 at 17,8 ft versus Sundance SV186 2011 at 18,5 ft. At 1 355 lbs and 1 450 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 150 hp, the Sundance SV186 2011 has a 60-hp advantage over the Sundance DX18 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 SV186 2011 carries 40 gallons versus 33 gallons in the Sundance DX18 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 DX18 2012 is rated for 6 passengers, while the Sundance SV186 2011 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Sundance DX18 2012 could be the deciding factor.
Bottom line: Choose the Sundance DX18 2012 if your priority is putting more people on the water - it handles 6 passengers and at 17,8 ft it has the deck room to back that rating up comfortably. The Sundance SV186 2011 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.