I own Marriott Weeks, Vistana Mandatory Weeks, and Hyatt.
Hyatt is my favorite. I am biased though because I live close to 4 resorts and don't have any trouble using points.
I love that it is a points system. This enables me to travel a lot more than if I was just dealing with weeks at a time. We probably do 10ish stays in Hyatt resorts and every year I have booked multiple rooms for family members to join us.
Here's the good:
1) Solid resorts. The floor is mid-tier Marriott resorts. The ceiling is best in class timeshares (Park Hyatt Beaver Creek, Grand Aspen, Siesta Key, Kaanapali).
2) Locations we enjoy and where a lot of other resort systems don't have much of a presence (Key West, Aspen, Carmel, Beaver Creek - on the mountain, Sedona)
3) Ski Destinations.
4) Reasonable-ish maintenance fees. The lowest cost 2 bedroom resort in the Marriott system is Marriott Grand Chateau, and fees are a shade over $1300 for a week. The lowest cost week in Hyatt is $1350 (Sedona). Other lower cost weeks are Hyatt Beach House, and Wild Oak Ranch. However, I don't have have pay a lockout fee to trade my Sedona week, and I don't need a separate interval account (since it's covered in club dues)
5) There is a wait list. If you can plan ahead, waitlist requests are not terribly difficult to get.
6) Points associated with a week are always transferable to resale owners.
7) Hyatt is an amazing trader in Interval.
There is a bit of an arbitrage opportunity because of the points based nature. For example, studios at nice resorts tend to stick around a lot longer than larger units. Because of this, they will often fall outside of the preference period where you can pick them up for 430 Hyatt Points. Considering that Diamon weeks get 2200 points, it's hard to beat that. I have sent my parents on multi-week trips to Maui Ocean Club, Kauai Beach Club, and Ko'olina because all they need is a studio.
Here's the bad:
1) There aren't many locations.
2) Availability isn't as good as some other systems.
3) You have a fixed week. This can be good, but it can be limiting.
4) I don't see a scenario where there will be a brand new resort built (yes, there may be some access to Welk, but I don't see a new resort getting built).
Here's the ugly:
1) Like
@dioxide45 mentioned, you are billed Club Dues in the amount of $157 per week. There is no discount for owning multiple weeks.
2) Maintenance fees have recently risen at a faster rate than other brands that I have owned in the past few years.
3) Anything other than Diamond weeks are at a bit of a disadvantage for single weeks owners. This is because in my experience the waitlist always prefers those looking for whole weeks.