Again, these are subjective opinions but what you've said about AWB and Darmian is basically blasphemy to me. You say you don't watch much of other players in the league but without being condescending here I'd question how much of Utd have you watched this season or in general?
AWB had a really good debut season and periods of form under Ole but it's clear as day that his overall footballing intelligence is lacking. He's a very capable ball carrier and passer but it's almost always in circumstantial instances i.e when a single opposition player is pressing him, he has an 'easy' outlet to pass or when the ball/play is in movement or transition as he has good instinctive awareness. However, when the ball is set, when there are pressing traps, when the time calls for more nuance both with (e.g passing between lines, pass choices, press resistance, angles etc) and off ball (e.g reading off the ball runs, keeping opposition offside, runs off his blind side etc), he is markedly bad. There's not really a debate when it comes to defensive nous or overall consistency over the two imo. I've been impressed with AWB at times and I've kept willing him to find that 'intelligence' but time and time again, he's shown he just doesn't have 'it'. See his part in the Brentford goal for case in point. Now I understand I may be harsh and it's unfair to extrapolate Dalot's form of this year compared to AWB's injury hit seasons of the past 2-3 but Dalot's overall peak and awareness is ahead for me. They're not really comparable at all if you actually want a team to play progressive, attacking and expansive football so for you to personally 'prefer' AWB when you've been criticising Dalot's lack of attacking output and how we are a such a poor team, is a bit contradictory.
Darmian had a good period of initial form under LVG and I think had good defensive and even some attacking instincts. It's stereotypical to say but he just had that Italian defensive reading of the game. You can tell he had some thought and nous to his play but he just wasn't athletic enough to really be dominant or effective on his own terms. He's closer to the Lindelof of right backs and in no way comparable as a 'variant'. It's like saying Lindelof and Van Dijk are similar players because they are both standoffish, are comfortable with the ball and like to read more of the game than make sliding tackles/get really aggressive shoulder to shoulder. On the surface that is true but VVD is twice as athletic (aerially, pace) with a way more composed and stronger mentality to play on his own terms with passing and dominating opponents. The difference between Lindelof to VVD is closer to the gap between Dalot and Darmian than those two are similar imo.
As for Valencia and Rafael, I don't really have a strong opinion because I thought they were both good players in their own times but Dalot is more rounded and therefore I would take him. However, that's unfair to compare as he's come 10 years later playing a much different game i.e playing out from the back, inverted etc.