I don't believe you're going to find any easy or definitive answer to your question. All are simlar but all have significant differences that set them apart. What is best for one person won't find the needs of another. Plus, there are so many different systems it would be impossible to compare and contrast all the systems. It would become so complicated that you may get frustrated and give up.
Still, I'll try to tell you what I can about the three that we belong too.
Hilton is a points based reservation system where owners own a deeded week. Hiton has different season and asigns different point totals to both the size unit owned and the season that it is owned in. Unit size determines the maintenance fee with Hilton and not the season the week is owned in. Many others base MF's on both size and seasons.
Hilton has very few locations where it has built Hilton branded resorts. It supplements those few with affiliated resorts either managed by Hilton (but not built by them) or resorts they feel are up to their standards. However, many of the affiliated resorts have limited availability for internal exchanges.
Hilton does have an exchange fee for internal exchanges. If you reserve your owned week during the home resort reservation window there is no charge but, you must reserve your entire unit. If you want to break up your unit (lock it off) then you must wait until the club reservation window (9 month mark) and pay a small fee.
Hilton exchanges through RCI if you want to exchange outside Hilton and it's affiiliates. RCI charges an exchange fee to do this. Hilton pays your RCI membership fee as part of your Maintenance fee's. It is not a full RCI membership and you must go through Hilton to make an exchange.
Marriott is another hotel chain that has timeshares. Marriott has many more Marriott built locations than Hilton. Marriott does not use a points based reservation system but uses a week for week exchange system. Marriott does not have an internal exchange progam per say but they do have a preference through Interval International for other Marriott owners wanting to exchange into other Marriott resorts.
There is a $89 exchange fee for Marriott to Marriott exchanges through Interval. Marriott does not pay your membership fee to Interval with also runs around $89/year. If you want to exchange outside of the Marriott system Interval charges an exchange fee of $135 for domestic exchanges and a higher fee for international exchanges.
You may lock-off your unit (if it is a lock off unit. Many Marriott's do not have this feature) 12 months in advance if you wish to split your week up. You may make reservations 12 months in advance if your a single week owner and, under certain circumstance 13 months in advance if your a multiple week owner. You may request exchanges into other Marriott resorts 12 months in advance.
Diamond Resorts International (old Sunterra) offers a points based internal exchange system, a simple deeded ownership without internal exchange priviledges and a trust based system with priviledges to exchange into any of the 19 trust based resorts or, if your a member of THE Club (points based internal exchange system) to any of the DRI owned, managed or affiliated resorts.
Diamonds deeded weeks allow you to stay at that particular resort based on the type of deed you own. If you want to stay anywhere else you'll have to exchange through one of the exchange companies. Depending on the resort week owned you my exchange some through RCI, some through I.I. or some through either. Simple deeded week ownership does not come with an I.I. membership. You must pay for that yourself.
Diamond also offers THE Club point based internal exchange system. It is not available to resale purchases unless you buy something from them or, in some cases pay a joiner fee (last reported was $2,995). THE Club allows you internal exchanges without paying an exchange fee to any of THE Club resorts. Some are only affiliated resorts with very limited inventory. Some are DRI developed resorts with most units available to members. THE Club has a membership fee of $159/year but it includes I.I. membership. If you want to exchange outside THE Club you must pay I.I.'s exchange fee. You spend points for exchanges through I.I. which gives you more flexiblity than exchanging week for week. Points may be used to purchase other services (FF miles, rental cars, airline flight certificates, discounts on cruises or to lower your MF bill). Points may be carried forward one year subject to THE Club rules.
DRI's trust based sytem does not give you a specific deed but gives you an interest in a trust which contains 19 different resorts. You can reserve a week at any of these resorts if you own enough points to reserve that week. There is not an exchange fee for this. Trust members may reserve a resort week at the 13 month mark (THE Club members may do so at the 12 month mark). Trust members may also be a member of THE Club, which gives them access to all 95 DRI developed, managed or affiliated resorts but, they'll also have to pay the $159 THE Club membership fee.
O.K. this is a VERY brief synopsis of just 3 out of dozens of differnt hotel and/or points based reservations systems. There are dozens more out there including Starwood, Hyatt, Bluegreen, Westgate, Disney and Wyndham to name a few. You'll have to do a lot of research if you want to attempt to understand all of them.
Personally, I suggest starting to take timeshare tours, ask questions and start to learn a little about each system. It's time consuming but it's the only way I can think of to really start to learn about each system before purchasing. Or, you can read posts hear and learn enough to know what's likely to fit your needs enough that you'll be happy and use that as a start. The learning curve has only begun and it will last a lifetime as the rules to the game keep changing.