Never seen the Yellowstone tandem in these parts. Cascade is pretty common, and I have a couple of friends that paddle them and love them as solos. Not the boat for me, but if those are the choices I’d go with the Cascade.
Personally, I’m not a big believer in the “one boat does it all” approach. If 80-90% of your time is paddling solo, I’d suggest getting a good solo boat first, then buying a cheap tandem (tons of them around), or hooking up with a buddy when you paddle tandem. I’m about your size, and the Yellowstone looks a little too small to me to be a good tandem anyway - especially if camping is involved.
I know you need to buy what’s available, but if you could find a Yellowstone Solo I think you’d love it. About the same length as the Cascade, but narrower through the middle. There are a bunch of royalex “river” boats that were made by different manufacturers before royalex’s demise - Bell had the Yellowstone Solo, Wenonah had the Argosy (and Vagabond), Mohawk had the Odyssey and Solo 14 (and 13). If they are for sale now they are usually pricey and go quick, but it might be worth a look.
I have had a Yellowstone Solo for years, and its done everything I’ve asked of it - lakes, rivers (up to class II, class III would be a stretch) and camping. It will cary a ton of gear for camping. I have it outfitted with bags and thigh straps for easy whitewater, but it rarely gets used for that (I have a whitewater boat).
There are also composite versions of these 14’ boats by a number of manufacturers. I also have the composite Wildfire, which is also a great boat:
If I could only keep one it would be a tough choice, but Yellowstone Solo would definitely be a contender.
I know I am off topic, but think about it - if not now in the future.