As YZER mentioned, what is the best head depends on your particular boat and how you use it. On a 26 foot sailboat or powerboat, the actual size of the head and if it is, electric, it's power draw, are paramount when making your decision. If you have a 90 foot houseboat, where space and power aren't a concern, then you want the best, most trouble-free toilet available.
Cost also comes into the equation. Marine toilets begin at about $129 and go all the way up to a couple of thousand. The Baby Blake manual toilet, made in England, brags about the fact that it is the most expensive manual marine toilet in the world. With their current price at around $3K, they are absolutely correct! The Wilcox-Crittenden Skipper head, as has been noted, is probably the best and also most expensive American manual toilet made - it's within spitting distance of $1K.
Electric toilets begin at about $350.00 and go up from there, depending on make, model and features. Being employed by Raritan, I tend to steer people to the PHII manual toilet - world famous as the best manual toilet in the world for under $500.00. On the electric side, the Raritan SeaEra offers the best "bang for the buck" at around $650 for the base model. These are retail prices I'm tossing out, BoatFix offers them at substantial discounts.
Other popular toilets are the Jabsco 29000-series manual toilet, that you'll find on many new smaller boats. It is the base model and usually has a lifespan of under 5 years. Then there's the Jabsco 37000-series electric macerating toilet. It works OK but is noisy enough to wake the dead. The VacuFlush heads are popular on medium size and larger power boats, and work very well. They generally run $2K+ in cost, and the VacuFlush people must install it or check out and approve your installation, in order for it to be covered by their warranty. The Blake/Lavac, also made in England, is a manual vacuum toilet that is very popular on midsize and larger sailboats, particularly those that cruise outside the U.S. In the U.S., replacement parts for them are difficult to find, and are very expensive, although the toilets are quite reliable - they rarely break down. The Techma electric toilet is gaining in popularity, largely due to its comparitively low cost. It is made overseas and is imported by Thetford/Wilcox-Crittenden. They have a pretty good dealer network in the U.S. for parts and service. Raritan's top of the line is called the Atlantes "Freedom", and is available in several configurations. Retail cost runs betwen $1100.00 and $1500.00. Then there's the old tried and true Raritan Crown Head, which has been around since 1965. There are crusty old captains who won't have anything else. It was the first electric macerating toilet on the market, and is still around, after 40+ years.
To sum it all up, marine toilets are like automobiles to a large degree. A Ford Escort will take you the same place as a Lincoln Town Car. If it meets your needs and budget, there you are. But if you have more elegant tastes and the funds to go along with it, you'll likely lean more toward the Town Car. It also has to do with personal favorites - is a Lincoln better than a Cadillac, or vice versa? Does anybody really know? But if you've had good results with one, you're more likely to get another one of those, rather than trying something different. Much of the same "logic" applies to marine toilets...