I think MIX Fold 2 is better since it's really lightweight for carrying and SoC is more powerful.
I don't use flex mode much but often use inner screen for reading books, so punch-hole free screen is comfortable for daily use.
The vivo's camera is better but I use Xiaomi 12S Ultra for photography so that's ok.
Also touch latency of MIX Fold 2's inner screen is far better than vivo (and even normal flagships), it's 37.6ms where vivo was 56.7ms.
Android smartphone Benchmark Charts; CPU, GPU, memory & storage performance, and touch latency - AndroPlus
Here's my benchmark results for each SoC and device. List of Benchmark Results AnTuTu benchmark is a popular Android benchmark app, but often falls victim
I prefer MIUI Fold as Ocean OS' battery saver is so bad.
I have to turn off battery optimization and enable auto-start but compared to Ocean OS, MIUI does respect user's settings and notifications comes smoothly.
Functionality of multi-windows are almost same.
Yes, there's call recording feature