The Triton Boats 1648 SFB 2009 is a flat-bottom design and the Triton Boats Ambush 18 2009 is a modified-V 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.
The power gap is worth calling out. Rated to 90 hp, the Triton Boats Ambush 18 2009 has a 55-hp advantage over the Triton Boats 1648 SFB 2009's 35-hp ceiling - enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
Both boats are rated for 4 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: The Triton Boats Ambush 18 2009 at 18,0 ft is the right call if deck space, comfort, and entertaining are top of your list. The Triton Boats 1648 SFB 2009 at 15,0 ft wins on trailering ease, likely lower purchase price, and simpler docking - a solid choice for a buyer who wants more boat for less money.