The Xpress Bayou 18 2012 is a flat-bottom design and the Xpress Rear Entry - XP21RE 2008 is a pontoon design, so you're likely deciding between two noticeably different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
On paper these two are close siblings in the size department - Xpress Bayou 18 2012 at 18,0 ft versus Xpress Rear Entry - XP21RE 2008 at 21,0 ft. Weight tells a clearer story for trailering families: the Xpress Rear Entry - XP21RE 2008 tips the scales at 1 800 lbs - 1 050 lbs less than the Xpress Bayou 18 2012 at 750 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 90 hp, the Xpress Rear Entry - XP21RE 2008 has a 40-hp advantage over the Xpress Bayou 18 2012's 50-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
For family outings this is probably the sharpest distinction between the two. The Xpress Rear Entry - XP21RE 2008 is rated for 11 passengers, while the Xpress Bayou 18 2012 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Xpress Rear Entry - XP21RE 2008 could be the deciding factor.
Bottom line: Choose the Xpress Rear Entry - XP21RE 2008 if your priority is putting more people on the water - it handles 11 passengers and at 21,0 ft it has the deck room to back that rating up comfortably. The Xpress Bayou 18 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.