Do you have a preference for Hilton or Vistana? if so, why?
First off, I agree with what
@sponger76 wrote.
The main reason to own one timeshare system or another is the location of the resort(s). "Buy where you want to stay" is in my mind the first rule of timeshares and while I sometimes use my weeks/points to stay elsewhere the best and easiest way to use a timeshare is to stay where you own. So I own Vistana and HGVC (and MVC and DVC ) because we want to stay at different resorts.
That said, legacy HGVC offers better opportunity to use your points elsewhere than most timeshare systems and many owners seldom or never stay at their home resort. It is in general (and IMHO) the best of the major timeshare systems as long as you understand its limitations and are able to plan 9 to 12 months in advance. In particular, HGVC truly excels if you want to do one of the three following things...
1) Stay at one of HGVC's major destinations - O'ahu, the Big Island, Carlsbad (CA), Las Vegas, Myrtle Beach (SC), Orlando, and maybe NYC. There is almost always plenty of availability at 276 days (~9 months) and you can just buy the least expensive deed anywhere in the system (taking into account both initial price and MFs).
2) Stay at any HGVC resort for a week at a time (usually Saturday to Saturday) in a particular unit size and season at least every other year. Because most people don't book Home Week reservations there is almost always availability at 12 months (except perhaps for the very highest of demand weeks - e.g. President's Week at a Ski Resort). For this you buy a deed for the unit, season, and resort at which you want to stay.
3) Stay in NYC or DC. Because the "by Hilton Club" (aka bHC) resorts in these locations have "Home Resort Priority" windows in addition to the "Home Week Priority" window there is a long period of time (typically 90 to 276 days in advance) during which resort owners and no one else can book short stays. In addition, only owners can make "Open Season" reservations (cash stays) and there is usually an owners lounge. You would need to buy at the resort though not necessarily the unit and season at which you want to stay.