The DFS one is a much more attractive shape although cheaper so maybe not as well made. I'd be careful about having chairs match the sofa, it all sounds quite matchy matchy and new at the moment, what old pieces of furniture are you putting in this room? And what is your 'disruptor' piece?
With black dining room furniture then of the dfs colour options I'd go for the navy velvet sofa or possibly pink depending on your wall colour choices. Can't see what the colour options are for the sofology one, if there's a green that might look good with black furniture. Your walls will need to be light with all dark furniture but if you wanted to go dark and dramatic then a light pink sofa would provide contrast. Or would you decorate the two halves of the room differently? Dark dining room and lighter sitting room or vice versa?
What I do is look on instagram to see how different people have done things. If you search for #blacktable then you can see lots of rooms with a black table and you soon work out which looks you like and which you don't. I like that it's not all designers so you see mistakes and different looks and see what is super fashionable etc so find it more useful in some ways than magazines where it all looks good.