The spec sheets list the FunTime FunTime 16 x 75 ft. 2008 as other and the FunTime FunTime 18 x 85 ft. 2008 as other, so check how each hull rides in the conditions you use before you decide.
For family outings this is probably the sharpest distinction between the two. The FunTime FunTime 18 x 85 ft. 2008 is rated for 17 passengers, while the FunTime FunTime 16 x 75 ft. 2008 caps at 15. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the FunTime FunTime 18 x 85 ft. 2008 could be the deciding factor.
Bottom line: Choose the FunTime FunTime 18 x 85 ft. 2008 if your priority is putting more people on the water - it handles 17 passengers and at 59,0 ft it has the deck room to back that rating up comfortably. The FunTime FunTime 16 x 75 ft. 2008 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 15 that costs less to run day-to-day.