Hi there, I think I remember you from a post asking to switch from fine art to diagnostic at UAL FAD?
I'm assuming that you want to pursue interior design. Have you compared the two courses' content and the location of each one - what are your preferences?
I'm going to put it out there that, for the 2024/25 cohort experience for diagnostic, it's exploratory into different disciplines, but not as much as you would expect. Each day is a different specialism, so you won't get much time to delve into each one, as well as there being a lack of materials available (largely paper and cardboard). The one day graphic design session, for example, consisted of cutting out letters, rearranging them and photographing them in different ways. This is the first cohort after the two UAL courses merged, so maybe it's a bit unpolished now and may improve for your cohort, but it's worth considering in comparison to parsons (who are also immensely renowned, though I don't know about them in as much detail).
Another thing to consider is if you finish the FAD, UAL guarantees that you can progress to one of their courses (not always the one that you want, but considering you want to get into interior design, it's much likelier than if you applied for fashion). This will increase your chances getting into the course by quite a bit, if that's one of your concerns. But honestly, if you managed to get a place at Parson's in the first place, I feel like you'd be successful if you applied directly for the UAL interior design course.
In terms of prestige, employability and networks, both are on a similar level but UAL could arguably be better. Take all of this with a grain of salt though - good luck and congratulations on your offers