Since I dropped Mahou Shoujo of the End a while ago I reread the chapters in which Anai Miu fights to get a refresher on her powers. Her
sword only stops time once
here, this scene plus the fact that she didn't use it to prevent the other enemies from running away at the end of the fight
here, and an enemy not being bothered by the sword
here leads me to believe the time stop sword has limits and only works as some kind of paralyzing beam (obviously, not in the literal sense, its still a time stop). At least, she obviously needs to be able to tag the target with it in some way to stop their time. Her merging with the parasite mahou shoujo also runs out after what can only be a few minutes at most, leaving her too drained to fight and in bad condition, as seen
here and
here.
Given that my opinion is the following:
1: While the mechanics of the sword's time stop are unclear it's clearly not an instant "always hits the enemy" time stop. Since I have no clue as to how it would interact with Accel's redirection (the mechanics might be simply be "point the swords's tip at the enemy") I'll assume it's not affected by it for simplicity. It would fall to whether she can tag Accel with it before her time limit runs out. Considering Accel's personality and fighting style she probably wins 8 or 9 times out of ten. My vote goes to Miu.
2: Forget the time-stop, Miu merged with the mahou shoujo is too fast for Accel and kills him easily. Mius stomps Accel in this one since his base durability is too low, again, my vote goes to Miu.
As a side-note, I think it should be clarified in Miu's profile that her Massively FTL+ speed is only in merging form (it needs to differentiate between normal Miu and merged Miu in general). We should also note the unclear mechanics of the time stop sword and the weakness of the merging running out incredibly fast and leaving her very weakened afterwards.