Hi Eylo and welcome. There is lots of knowledge and advice to be gained here on the forum but in this case I think that your question is straightforward.
Which selection has the superior sound quality is easy; Vivaldi was a significant upgrade from Scarlatti and v.2.0 of the Vivaldi firmware provided yet further distancing from Scarlatti in sound quality terms , not least given the new Map options for Vivaldi (and Rossini) which allow the processor to run at double speed.
However you also need to take account of what facilities the options provide and their interoperability.
Firstly none of the second generation wordclocks ( Puccini, Paganini and Scarlatti) are fully compatible with third generation products ( Bartok, Rossini, Vivaldi). This is because the earlier clocks only provide a single frequency output at a time. Vivaldi etc. require a dual wordclock input each at running 44.1 or 48 kHz or integer . This is to provide automatic switching when sample resolutions chnage - as they may do frequently when using streaming services. Without the dual output you would need to manually reset the wordclock output each time the incoming sample rate changes. So Scarlatti wordclock + Vivaldi DAC is not a great mix.
The subject of streaming services also relates to the Vivaldi Upsampler. Scarlatti Upsampler only does what it says in its name. Vivaldi Upsampler is also a network player providing, with its dCS Mosaic controller, replay of local files from NAS, Qobuz, Tidal, Spotify, Deezer and a vast selection of internet radio stations. No Bridge is required NB: the sound from the Vivaldi Upampler’s network player is somewhat better than the Network Bridge was ( yes I have owned both).
Given the option to purchase either of your options there is no contest - it’s a no brainer IMO- the two Vivaldi boxes and maybe go for the matching wordclock later if and when you can afford it.