Hi John,
As Doug mentioned Wikitree is different from many other genealogy sites because we are aiming to create a single (well sourced) family tree that everyone can contribute to rather than maintaining a large number of individual family trees. Some of the benefits that can be realized by having one collaborative tree are:
1) creating one profile per person with numerous contibutors working to constantly improve it is a way to 'stem the tide' of bad genealogical information - If you use FamilySeach or Ancestry or other sites I am sure you are familiar with cases where one researcher makes an error or unsubstatiated conclusion which then propogates to other trees to the point where the 'error' is the first thing returned in every search. By 'pooling' profiles together and encouraging collaboration there is an opportunity to address the errors 'once and for all'. With that said, since we allow upload of Gedcoms, Wikitree is also often a 'victim' of that bad information and we do spend quite a bit of effort on fixing errors introduced from other sites.
2) allowing many interested people to colloborate on each profile can help to limit the duplication of effort in researching and analyzing sources that have already been found and to allow re-evaluation when new facts are found; it also means that people who have access to different sources than you do can bring new pieces to the puzzle - perhaps a cousin has inherited a photo or original record you would not otherwise have known about or had access to. Of course people being people, collaboration can be a real challenge in and of itself.
3) As the tree grows it is increasingly likely that users will find relationships to other researchers, and can further coordinate their efforts on solving the inevitable family mysteries.
Wikitree also has excellent search engine optimization so that profiles frequently top the results on internet searches for specific names - what people can access (and edit) is governed by privacy settings - and to support our goal of building one collaborative tree we have rules about privacy settings that largely depend on the age of the ancestor. Older profiles must be open, meaning any Wikitree user can edit them - it means they can be improved, although there is always the risk people will add errors. (the best way to combat that is to point out commonly held facts that have been disproven or are not substantiated)
As far as sharing your existing research, GEDCOM can be uploaded to Wikitree (with limits on number of people per upload), however when a large number of research is already completed many people find it an onerous task to go through the matching and merging process (i.e. trying to limit the number of duplicate ancestors in the one shared tree) and then 'cleaning up' the profiles to remove 'gedcom artifacts'. I personally hand craft each profile so I am not overly familiar with gedcom uploads but as far as I am aware, any images would have to be uploaded individually - I imagine the DNA results would also need to be redone.
Something you should absolutely be aware of in making your decision.
Once you upload your research, as Doug also already mentioned, it becomes part of 'the one family tree' and you will no longer have ownsership (i.e. absolute control) over all of it - and perhaps more importantly you will not normally be able to delete it. The reason for this is rooted in the collaborative nature of Wikitree - quite simply, if a profile already exists then other researchers should not create a new profile, but add their research to the existing profile - if you were allower to delete the profiles you added, you are potentially making holes in the research others would have contributed if the profiles you created did not exist.
I definitely prefer Wikitree over other sites I have looked at and/or tried for documenting and sharing my research - my research has already intersected with others here on Wikitree; their existing contributions limited the effort I needed to expend on certain branches, and I have been able to spend that time adding new information to their existing work and to researching and documenting other branches that are not on Wikitree.
