Both the Crest II 30 2007 and the Crest Upper Sundeck 27 2008 are pontoon designs, both built in aluminium, 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 - Crest II 30 2007 at 30,0 ft versus Crest Upper Sundeck 27 2008 at 27,0 ft. Weight tells a clearer story for trailering families: the Crest Upper Sundeck 27 2008 tips the scales at 3 988 lbs - 1 158 lbs less than the Crest II 30 2007 at 2 830 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 - 150 hp for the Crest II 30 2007 and 150 hp for the Crest Upper Sundeck 27 2008. 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 Crest II 30 2007 is rated for 18 passengers, while the Crest Upper Sundeck 27 2008 caps at 15. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Crest II 30 2007 could be the deciding factor.
Bottom line: Choose the Crest II 30 2007 if your priority is putting more people on the water - it handles 18 passengers and at 30,0 ft it has the deck room to back that rating up comfortably. The Crest Upper Sundeck 27 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.