Based on the pictures, I would probably choose the red roan. Of course, I do not know their temperaments, pedigree (which doesn't really matter if you're riding trails) and its a bit difficult to judge their confirmation from these photos.
The bay filly looks a little downhill with a straighter shoulder, perhaps a slightly roached back, but this could be the angle that the picture was taken at (and she's grazing). Her hind pasterns look a little weak in the first picture of her, but again, this could be the angle.
I like the roan filly's head, but her throatlatch could be a bit cleaner. I like the angle she has to her pasterns and hooves. And her insane cuteness is an added bonus