I don't know if this is an unpopular opinion, but... I prefer Lou Fa xD
I started respecting Lou Fa's affection for Allen after reading "Maiden's Rhapsody".
Before the Arc arc, I thought it was heavily implied that Lenalee and Allen would end up together (her prophetic nightmare about the ruined HQ and she's crying alone with Allen laying on her lap, the train scene when Allen bows to apologize and Lenalee puts groceries on his head; when at night, Allen's eye bothers him and Lenalee holds him back from retreating into the darkenss, etc.)
After the Arc arc, those kinds of overtones sort of disappeared and it seems much more like a sister-friend relationship, if that. For example, Ch. 184, when Allen slips into Nea for a moment and Lenalee are alone in the room together, there isn't any romantic feelings at all. Another obvious example would be when Allen left the Order and Lenalee had nothing to say. To be honest, I was really disappointed when Lenalee didnt even say "Don't go" as a friend...
Rather there are lots of interactions with Lenalee and Lavi. For example, Ch. 149, Lavi saves her from Leville when Leville tries to force her to get her Innocence and fight. In general, Lavi seems to always be looking out for Lenalee and saying supportive words, although there isn't any signs that Lenalee notices Lavi lol. Overall, most of the Order tend to look out for Lenalee so she could be uncanonically shipped with a lot of people.
In terms of relationships, Bak has a humorous crush on Lenalee, Lou Fa has a crush on Allen, and Timothy has a crush on Emily.
Canon-wise, Marie and Miranda, Kanda and Alma, Krory and Eliade.
I feel like forgetting some relationships. Maybe the Fou and Bak?
In terms of my preference, I rather see Allen with someone who suits him. At first I thought that was Lenalee, but it seems pretty clear that they both are not ready to have a relationship and it isn't very obvious whether they feel attracted to one another. By that I don't mean, the in-frequent, "Oh Lenalee is cute" comment but rather something closer to the loyalty, committment, and love that Allen has for Mana and Lenalee has for her brother. Allen and Lenalee both have "a most important person" and I can't imagine at all, for now, that it would be each other. It would have been really simple for Hoshino-sensei to put a small blush here and there to indicate attraction, but I think this isn't that kind of manga. As someone else put it on the forum, "this isn't a story about Allen finding a girlfriend".
I think since Allen is so broken and has so many problems, that he would need someone who helps him. Lenalee in a way is also extremely fragile. It would be nice if they helped each other out which was sorta happening in the begining of the series, but now it seems like Lenalee can't commit to being there for Allen, even as being a friend as much as Johnny is.
As for Road, I think her motivations towards Allen is currently unclear and the fact that their first encounter started so sadistically makes it hard to imagine a canon relationship. Her affection towards Allen is cute though and its sweet how she tries to help him out.