The Starcraft Marine 1620 FLSS 2008 is a modified-V design and the Starcraft Marine Stardeck 180 Fish 2012 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 - Starcraft Marine 1620 FLSS 2008 at 16,0 ft versus Starcraft Marine Stardeck 180 Fish 2012 at 18,8 ft. Weight tells a clearer story for trailering families: the Starcraft Marine Stardeck 180 Fish 2012 tips the scales at 1 550 lbs - 1 042 lbs less than the Starcraft Marine 1620 FLSS 2008 at 508 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.
Both boats share a closely matched power ceiling - 40 hp for the Starcraft Marine 1620 FLSS 2008 and 50 hp for the Starcraft Marine Stardeck 180 Fish 2012. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup.
For family outings this is probably the sharpest distinction between the two. The Starcraft Marine Stardeck 180 Fish 2012 is rated for 8 passengers, while the Starcraft Marine 1620 FLSS 2008 caps at 6. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Starcraft Marine Stardeck 180 Fish 2012 could be the deciding factor.
Bottom line: Choose the Starcraft Marine Stardeck 180 Fish 2012 if your priority is putting more people on the water - it handles 8 passengers and at 18,8 ft it has the deck room to back that rating up comfortably. The Starcraft Marine 1620 FLSS 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 6 that costs less to run day-to-day.