When two boats share the same hull type — in this case both the Zodiac 550 2009 and the Zodiac II C 2009 are inflatable rigid designs with inflatable construction — 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?
Both boats share a closely matched power ceiling — 120 hp for the Zodiac 550 2009 and 115 hp for the Zodiac II C 2009. 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 Zodiac 550 2009 is rated for 11 passengers, while the Zodiac II C 2009 caps at 9. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac 550 2009 could be the deciding factor.
Bottom line: Choose the Zodiac 550 2009 if your priority is putting more people on the water — it handles 11 passengers and at 18,1 ft it has the deck room to back that rating up comfortably. The Zodiac II C 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 9 that costs less to run day-to-day.