I match the polyleader to the task at hand, as I use shooting heads a lot then they make a useful transition between line and leader. I do not use anything other than slow sink and floating lines for salmon fishing so the tips I use are reflected in the fact that the line I am casting doesn't 'get down much' therefore I need to balance my outfit with 'tips' that will achieve the task for me.
As a rule of thumb I (personally) want my polyleaders/tips to be sinking.
On smaller rivers I very rarely fish anything other than a sinking (no floating or intermediate) polyleader as 9 times out of 10 I want my fly to get down and get down quickly.
Length of polyleader (for me) is largely dictated by the type of line I'm using. As I do a fair bit of single handed Salmon fishing then (depending which falls out of my bag/pocket etc first) I use shorter polyleaders from Airflo and versitips from Rio on the front of a SLX. Again, I don't really bother much with anything other than sinking leaders, I have no use for a floating one or an intermediate unless I feel my 'presentation' is suffering on the rare occasion that I fish a full floater but even then I'll make sure I'm using a 'proper' tapered leader making the floating polyleader redundant in my eyes.
When it comes to big boys toys on the double hander then it's the big leaders and, again, it's nearly always a sinker as I feel that's of more benefit to where I fish the most and reflects my personal choice of of using floating or very slow sinking lines/heads - the fastest sinking salmon line in my possession is a Mackenzie intermediate shooting head.
With that 'sorted' I adjust my choice of polyleader to the conditions. For example, I turn up to my favourite pool and the river is:
1. "flowing like buggery" - leader choice: feckin fast sinking.
2. "flowing quickly" - leader choice: medium sink.
3. "next to no flow" - leader choice: back to the pub.
In the scheme of things it's not brain surgery
H