I have come down to a choice between the F50R or the D55.
why is your choice between those models?
much depends on the way you play the guitar. do you strum with a flatpick? play single string lead lines? fingerpick with bare fingers... or picks?
i play fingerstyle and dearly love the sound of a good d-55 or f-50r. string make a big difference, but if i were to generalize, i would say the tacoma d-55s i have played have had a rich, smooth, homogenized tone. i can't recall playing a tacoma f-50r, but i have played a few westerly f-50rs and, by comparison to the d-55, i find them a bit brighter in tone and a bit more articulate note-to-note.
this is purely subjective and since you must buy mail order i would encourage you to seek a retailer that offers an approval period.