I was browsing their site earlier and IIRC the Black isn’t included in the sale
That's quite a wide range of sizes and prices in that list, and some variations in colour.
What order of priority would you place on Carat weight, Colour, Clarity and Cost?
If you can work out whether you'd prefer larger and lower colour, or smaller and higher colour, or to spend less overall and have lower colour and smaller size, that will help your decision-making process.
The Signature and Black lines will both look excellent, so you do not need to worry too much which you choose. IIRC the Black stones have some minor tweaks of minor facets, with the aim of increasing brightness and reducing some contrast (I *think* - I can't remember exactly now) but they will both perform very well.