the back and spine - how straight?

[Falcor]

OK, I've heard two advices:

1. ALWAYS keep your back straight. When doing your stances, try to keep your spine vertical.
** When transitioning from horse to bow, keep the back/spine upright **

2. ALWAYS keep your spine straight. When doing stances, try to keep your back in-line with your hips.
** When transitioning from horse to bow, keep the spine straight, but angle your torso such that from the top of your head down your neck, your back, your butt, your leg and all the way down to the rear foot that is flat against the ground, you get one straight line. This may mean that your back may be "tilted" but as long as you're not leaning, and your spine is straight and in line with your rear leg, it's good **

What do you guys think on this topic?

[Falcor]

Oh, I should add that the two advices were not mutually exclusive, at least in the context that I heard it. It was more along the lines of "do #1 most of the time, but do #2 sometimes when the technque warrants it."

OTOH, I've also heard "Never do #2, always do #1".

[Xdr4g0nx]

the way sifu explains it to us is this:
imagine a string is tied to the top of your head (if u want to be gruesome imagine it is tied to a nail that is nailed in the middle of your head.) the string is connected to the ceiling. when u transition your head should feel like its floating which in turn will keep your spine in the correct position.