I don't have a specific recommendation for pool shape based on your yard shape. It seems it would accommodate either with ease from a design perspective. What you do around the pool regarding decking/landscaping will determine how well it all ties together.
I do however have an idea that you may not have thought about. Our backyard is also a continuous slope downward, though where our pool is, the slope looks steeper. You could consider having the retaining wall above the pool instead of below it, not far away from where your deck/hot tub area ends. A few benefits of this are as follows:
- You get to see the beautiful retaining wall all the time from the pool area - creates nice ambience.
- Your pool seating area has a nice backdrop to it, where your chairs/lounges will feel like they aren't sitting out in the open.
- The lower side of your pool may be mostly at ground level so everything you play with in the pool, balls, etc. won't go over the retaining wall and have to be retrieved. They will stay closer at hand.
- Your decking on the lower side of the pool will not be installed on back-filled material, which has a tendency to settle over time.
- You will get massive amounts of extra seating free of charge.
- Your seating area will be that much lower and therefore, out of sight of the neighbors prying eyes. We like our privacy as you can tell from the side landscaping. When you are seated out on the deck near your proposed retaining wall, you will feel as if you are on a stage for all to see.
- The pool will feel more connected with the rest of your yard/play area behind.
Here is view of ours from the downhill side as a visual for the possibility. Our pool was still 2-3' out of the ground on the lower side, with the ground continuing downward as well. Our landscaped area below the pool slopes down massivly to account for that. I don't think you will have that nearly as much. Our shape too, as above, was a nod to practicality because we wanted an autocover.
Either way it will be beautiful, I just wanted to highlight a different option and the benefits of it.