Both the Mariah G21 2011 and the Mariah R20.9 2009 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 G21 2011 at 21,4 ft versus Mariah R20.9 2009 at 20,0 ft. At 3 600 lbs and 3 700 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 300 hp, the Mariah G21 2011 has a 30-hp advantage over the Mariah R20.9 2009's 270-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load. Both carry nearly identical fuel loads - 35 gal and 38 gal - so range won't be a tiebreaker here.
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 G21 2011 and its 300-hp ceiling. If fuel economy and quieter running matter more than top-end speed, the Mariah R20.9 2009 with its 270-hp rating is the more economical daily driver.