I'm a swede but are generally harder judging against my own countries player than to others, but yet some will think I'm biased...
Peoples obsession with Maguire ahead of Lindelof are laughable. The only thing Maguire has over the swede is heading (which are the swedes worst skill), and to big that big and so bad in the air as Maguire still is a mystery. I very much doubt that we had conceded 4 goals with Lindelof instead of Maguire against Brentford, simply because his acceleration and pace (even though he isn't the fastest in the world) is way better. I also thinks that Lindelof is a better leader, he's the captain of the swedish national team and you can see that it's often him who talks the most in the center of the pitch in United's games.
Lindelof is not a great defender. certainly not for a club of United's stature, but still better than media and pundits "favourite" in Maguire. Lindelof always gets the shit when they play together, rarely Maguire, even if it obviously not his fault.
With that said I don't think Lindelof and Martinez is a good pairing. First of all the strenght in the air is weak, none of them are a good header of the ball. Both of them rather wants to play out of the back than hoofing if possible and both wants to put pressure higher up in the pitch. They are more similar to each other.
Though I actually think that Lindelof could do a good job as a right defender instead of Dalot. He has a better right foot (often takes the free kicks in Sweden and has taken penalties there) and actual football brain: I'm not sure it would happen but he would do much better job there than Dalot I believe.
With the current players I would like to see Lindelof - Varane - Martinez - Malacia as our back four. I've never rated Maguire, not in Hull, not in Leicester and most definately not now in United. I think he's the worst (of the ones who could count as starters) central defender we had during for the last at least 30 years. And we payed 80 mil. for him, lunatics...