What is the proper way to pick?

It really all depends on the tone your chasing for a particular song. You want it dark? Pluck by the neck. You want it bright and snappy? Play by the bridge.

 

This is going to sound like a dumb answer but the best way to pick is however, it works for you. Everybody's anatomy is slightly different. If you are comfortable and it sounds good, that's all that matters.

 

Like Phalex said, it depends on what sound you want, so you'll probably end up using multiple methods. For instance, if you want to mute the strings, you'll have your hand near the bridge and you'll probably end up keeping it pretty much in the same spot, but pivoting at the wrist to hit the different strings.

 

Again, the answer is 'whatever works for you' really. I prefer moving my thumb from the pickup to the E and back depending on the string I'm playing, but many players prefer to keep it anchored.

Both are 'correct'.

 

Also, this is the first sticky in the sub forum, I think it addresses what you're asking

http://www.talkbass.com/forum/f21/floating-thumb-techniqe-230685/

 

Drop your hand, try not to reach down from a fixed point.
Check out the link, all the info in the video should be considered, but your relevant info to consider is at 3.45

 

Try both. I personally will move up and down strings when using a pick. When using fingers I will stay put. Playing with thumb I guess I move ( he says while trying to play in front of mirror because he doesn't know ) and obviously slapping I move up an down.