Both the Mariah R21 2011 and the Mariah SX21 Bow Rider 2008 are modified-V designs, the first built in aluminium 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 - Mariah R21 2011 at 21,4 ft versus Mariah SX21 Bow Rider 2008 at 20,0 ft. Weight tells a clearer story for trailering families: the Mariah R21 2011 tips the scales at 3 400 lbs - 400 lbs more than the Mariah SX21 Bow Rider 2008 at 3 000 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 power gap is worth calling out. Rated to 300 hp, the Mariah R21 2011 has a 40-hp advantage over the Mariah SX21 Bow Rider 2008's 260-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Fuel capacity breaks the other way: the Mariah SX21 Bow Rider 2008 carries 44 gallons versus 36 gallons in the Mariah R21 2011. On a lake day that's negligible, but for coastal cruising or long reservoir runs the extra range matters.
Both boats are rated for 10 passengers - a good fit for a family of four or five plus guests. Comfort at capacity is another matter; the longer hull typically means more seat options and better weight distribution.
Bottom line: Performance buyers should lean toward the Mariah R21 2011 and its 300-hp ceiling. If fuel economy and quieter running matter more than top-end speed, the Mariah SX21 Bow Rider 2008 with its 260-hp rating is the more economical daily driver.