The most cost-effective form is where a group of individuals decide to purchase an asset jointly. They then decide on the exact asset to be purchased, draw up ownership documents (perhaps with the help of a legal firm) and purchase and manage the asset themselves. This avoids the sometimes substantial profit-margin that developers charge when selling fractional properties. This approach does have disadvantages, e.g. the amount of paperwork involved and the possibility of falling out with your fellow fraction owners (over cleaning, maintenance etc.)
Second in terms of cost-effectiveness would be a developer or owner-led scheme, where the individual fractions were being sold direct from the developer/owner (but where there were no expensive additional services bundled with the purchase). There will have to be a profit-margin associated with this type of arrangement, since the developer/owner is incurring additional legal and administrative costs. If fractions can be sold individually (without all the fractions of an asset being sold) then they are also taking the risk of having unsold fractions tying up their capital.
The above schemes blur into the next category, which I will call clubs. These are sometimes called Ownership Clubs, Private Residence Clubs, Destination Clubs etc. etc. Where they differ from simple developer/owner-led schemes is in the level of luxury/services provided and (sometimes) in the level of ownership. None of these terms have a particular legal meaning so it is up to the purchaser to investigate issues of ownership, booking arrangements, exit arrangements etc. A the extreme end of this group there are some similarities with