I have not mastered this lens for interior shots. I would not use this lens for real estate work, although I understand there are pros who do great with it. Here are a couple of bad photos of small rooms in my house:
Were I to buy either of the lenses, I would definitely choose the 24mm. But I have mostly satisfied my curiosity about them, and would find it hard to justify the cost for the small amount of use they would get. If I still got work from realtors, for example, then the situation would be different.
There is no doubt the 17 is much more difficult to use effectively than the 24, indeed I use the 17 with a 1.4TC giving me a 24 more often than I use the 17 alone, but I need 17 often enough to justify it over the 24.
If people were looking at the TS-E's primarily for landscape I'd say get the 24 and when you want wider stitch, if you are real estate/architectural shooter and can only afford one then get the 17 and TC's as the IQ from that combination is plenty high enough even for particular clients. One of the downsides of the 17 is the cost, hassle, and bulk of filter solutions which are much more widely used by landscape shooters than real estate shooters.
I was very deliberate about getting my TS-E lenses, I can't justify more than two and I already had both 1.4 and 2x TC's and I shoot a lot more real estate and architecture than landscapes, so for me the TS-E 17 was the obvious choice. I have now augmented the 17 with the TS-E 50 which I use for real estate exteriors, product and macro shooting, with those two lenses and TC's I have ended up with very high quality 17mm, 24mm, 34mm, 50mm, 70mm, and 100mm TS-E's.
I'm glad you ended up having fun with your rentals, always good to push ourselves in whatever we have an interest in.