Convince me that Marriot or Wyndham after 10 years is the better choice.
Better is subjective. Oddly, you've nearly hit on the three systems my family owns.
We bought a platinum week at Marriott Mountainside in the early aughts (don't remember when, but we'd owned for years before I had my DS in '06). We'd been going to Park City and staying as close to the slopes as we could get every year for a week since 1992, and after 2 years of paying hotel prices for a 1 bedroom at Mountainside when it was built we were sold. We bought direct retail, a half share (every other year) and soon added on a full platinum week since my mom likes to do 1 week one year and two weeks the next. Considering unloading one of the contracts due to my mom getting older, the grandkids schedules are more crowded now, etc. But we've gotten an extreme amount of value out of those weeks and II when we MVCI was associated with II (we ended up picking up a lot of bonus/extra summer weeks over the years through II once we discovered how beautiful it was to hike in non-ski season).
DVC doesn't have any options to pick up extra time other than transferring in points. We considered switching over to points but get a better value out of weeks and its the way we like to vacation there (slopes are much less crowded during the week, esp Sundance week, so we don't ski on weekends). Haven't checked the value of the contract lately but we'll probably get back a little less than what we paid for it if the prices are around the same as we looked at pre-pandemic. For the platinum weeks we want we have to wake up at in the middle of the night Hawaii time 13 months out or they're gone. Not fond of that.
I had coworker who bought Marriott and then sold at a loss later when they realized they weren't using it. For us it's been great because we already vacationed in a way that suited MVCI, and Park City prices just kept going up so our maintenance fees there still make us feel like we have a bargain property compared to hotel prices. We rarely get pitched bc we travel without spouses and they want your spouse there to buy with you (even though the contracts are specifically not in my dad's or my spouses' name, because they hate skiing). I'd have to do the math, but we've probably gotten the most "value" out of this one due to the insanity of the hotel prices that we probably would have paid to be slopeside anyways over the years.
I bought my first VGC contract in '08 before it opened, then an add-on resale in '10. I could sell those contracts for over triple what I paid but I'll never sell. Love the flexibility as the kids have gotten older of being able to switch from weekdays to weekends, etc. Love Disney, love my home resort, will use it until it expires. Wish there were more options to get more reservations than OTU points, and the lack of being able to borrow/bank more than a year is sometimes limiting. I always book 8-11 months out, if I know my dates I usually book at 11, and I've gotten studios that I've waitlisted around the 8 month mark about 60% of the time. If we didn't own, I probably wouldn't have stayed on property more than once or twice/ would have gone to one of the nearby Marriott hotels or Best Westerns to feed my DL addiction, so it's less of a "savings" vehicle as an "upgrade my vacation" vehicle.
Picked up a small Worldmark contract in '15-ish, resale. It was cheap (I paid $2k for 6k points annually), it had locations I wanted (mostly I'd wanted the Maui location bc its near my elementary school and my folks' house instead of being in more touristy parts of the island since I was tired of sleeping on their couch when I visited, but also having the California locations be in places I wanted to weekend was appealing).
I keep thinking I'll sell the contract any day now, but then I find another use for the points. I've always gotten what I wanted via wait-list, never book more than about 6ish months out, and have been consistently impressed with the locations (other than Anaheim), even though the units are ... just okay. All the rooms are functional no-frills feel, but have been in exactly where I want to be when I visited Vancouver, Tahoe, Monterey, Kihei, San Diego, etc. This might be because I like going to the parts of the cities where locals live when I travel close to home (and am often visiting friends and family). I use the Monday Madness to add on a lot of extra nights at properties like Solvang and San Diego. Banked points last longer than DVC which was nice during the pandemic. Fell in love with the Vancouver property even though ending up there was a complete accident I'd just needed a pre-repo-cruise hotel that was cheap, definitely want to go back and spend more time there. Wyndham now owns Worldmark and a lot of owners think the quality of the system has gone down because of it, but I didn't own pre-Wyndham (or they switched over very shortly after I bought, not sure which), and I never trade to Wyndham, so don't know much about that. The sales pitches are annoying but avoidable (only made the mistake of going for the $100 Amex GC at Anaheim once). Housekeeping tokens are annoying, but when you can use bonus weeks/Monday Madness, etc, I've never had to buy one so I guess not annoying enough to deter me from using my points the way I want to.
Hope that gives you an idea of some of the pros (and slight drawbacks) of each of those systems. I've found all three to be great for my purposes, but each one had a different idea in mind when I got them.
