Here's my standard list of pros and cons for Placencia and Ambergris Caye. I agree with Barbara -- if you're going to split, I'd say choose either Ambergris Caye or Placencia, (or substitute Caulker for Ambergris Caye if you're budget-oriented) and add Cayo.
--Lan Sluder
>>
A few of the differences between Ambergris Caye and Placencia:
AMBERGRIS CAYE (often referred to as San Pedro):
* The biggest island in Belize (originally a peninsula jutting down from the Yucatan) -- northern Belize
* Settled by Mestizos from Mexico
* Most popular destination in Belize (for many good reasons)
* 7,000 residents on the island
* Mostly sand streets, no building over 3 stories
* By FAR Belize's widest selection of restaurants and hotels
* Among the best top-end hotels: Victoria House, Mata Chica and Portofino and condotels Villas at Banyan Bay, Banana Beach, The Palms, Xanadu
* Among the best mid-range lodging: Mayan Princess, Corona del Mar
* Among the best budget lodging: Ruby's, Pedro's Backpacker Inn
* Some shops, sizeable groceries, lots of bars and places to hear live music
* Very nice beaches though like all beaches inside the reef somewhat narrow and with some goop bottoms and a good deal of seagrass
* Beaches along most of the Caribbean side (20+ miles)
* Reef just a few hundred yards offshore
* Decision required about locations -- more remote North Ambergris requires water taxi, south end or in/near town
* Lots of snorkel tours and day trips to the mainland to visit ruins
* Good diving locally and excellent diving on day trips to Turneffe or Lighthouse atolls
* Get there by flights from international (US$47) or municipal airstrip (US$26) or by water taxi (US$14)
* Safe and friendly (though usual cautions are in order, and with growth crime is increasing some)
* Transportation on the island -- bikes, rental golf carts, cabs, water taxis
* Hotels from US$15 to $500+ a night
* Small condos and vacation rental houses available US$100 to $500+ a night
* Great golf available on nearby Caye Chapel (but expensive -- US$200 a day)
* Tennis available at sports club and at a couple of hotels
* Water -- safe to drink from municipal system or RO/wells as remote resorts
* Good fishing -- tarpon, bonefish and other
* Very little snorkeling from shore (best snorkeling requires a short boat ride to Hol Chan Marine Reserve (including Shark-Ray Alley)
* About the same amount of rain as Atlanta, Ga.
* Significant new development taking place especially from town to about 2 miles south of town
PLACENCIA:
* 16-mile long peninsula in southern Belize (Stann Creek District)
* Access from Belize City via road by rental car (3 1/2 hours, US$55+ a day), bus (6+ hours, US$8), air (40 minutes, US$70 from international, US$55 from municipal)
* Placencia village is 25 miles from the Southern Highway on an unpaved road
* Two villages on peninsula -- Placencia (Creole) and Seine Bight (Garifuna)
* Peninsula population about 3,000
* Wide choice of hotels from budget hotels in Placencia village to upscale resorts farther north
* Hotels from around US$15 to $400+
* Few condos but some vacation rental houses, US$100 to $300+ a night
* Among the best to-end lodging: Inn at Robert's Grove, Turtle Inn
* Among the best mid-range lodging: Kitty's, Mariposa, Barnacle Bill's, Nautical Inn
* Among the best budget lodging: Tradewinds, Ranguana, Seaspray, Manatee Inn
* Some good restaurants in Placencia village and elsewhere, though most of the better restaurants are at hotels
* Transportation on peninsula -- taxis or your rental car
* 15+ miles of very nice beaches along Caribbean side -- best beaches on mainland but not much different from those on Ambergris Caye
* Day trips to mainland to visit Cockscomb jaguar preserve and to Maya sites near Punta Gorda
* Day snorkel trips -- reef is 15 miles out, though snorkeling is also available at islands and patch reefs closer in
* Little snorkeling from shore
* Few shops, only small groceries
* No golf; tennis for guests at Robert's Grove
* Safe and friendly (though usual precautions are in order)
* Water from municipal system safe to drink
* Good fishing for permit, bonefish, tarpon and other
* Access to small islands offshore for day or overnight visits
* Good to excellent diving on day trips
* Limited nightlife
* More rain than Ambergris Caye (especially during rainy season June - November)
* Sandflies can be irksome
--Lan Sluder <Fodor's Belize & Guatemala, San Pedro Cool, Adapter Kit Belize, Belize First Guide to Mainland Belize, etc.>
AmbergrisCaye.com 
