For cost efficiency, I would either go SSR or AKL. SSR because you can book any cheap room, including OKW. AKL has the value rooms. These are incredibly difficult to book, but if you can pull it off, it will flip the math. Even if you can only pull it off a couple times, it would flip the math. AKL value 1BR isn't that hard often, surprisingly. One of the best values in the charts. SSR is a beast, no problem to get a studio.
The chart does the heavy lifting for cost efficiency. The cheapest rooms can be some of the most difficult to book in the whole system, but they do pop up. Your goals of "easily book" and book the cheapest rooms are going to be difficult. Booking these rooms requires work and walking and messing with this all the time or luck.
The middle ground of rooms that are on the cheap-ish side and easy to book would be the AKL standard rooms. There are a whole lot of these, and they are on the cheap side of the charts. Pretty close to OKW/SSR in point cost, but longer contract.
Another idea is CCV, especially if you are buying for long term. It doesn't have a lot of studios, this can be difficult to book. But CCV is good point value for SUCH a long contract, and it matched the BR chart when it launched, so it has a unique combination of both a retro chart and a really long contract. And I think CCV is a good buy for sleep around points now. I don't even like WL, and I've seen a couple contracts I was tempted by.
I'd also consider BLT. I think it's undervalued in resale right now, location is absolutely killer, and the chart isn't horrible. The 1BR is difficult to book because it has two bathrooms, which makes it an excellent room. To get the cheapest point category, you have to have BLT points. This will be a little more than SSR/AKL, but it is an idea. Be sure to look at charts when you are doing your math!
If I were on the fence, or planned to sell soon-ish, I would much rather be selling BLT or CCV in ten years than AKL/SSR.
I found this chart helpful:
https://www.dvcresalemarket.com/blog/best-economical-dvc-resorts-to-purchase-spring-2022/