How to determine return pump size?

[moocow]

I have a 58 gallon tank, aiming for about 250-300 GPH.
The distance from the pump to the outlet in the tank is about 5 feet.
Of course there will need to be either 90degree elbows, or 45's.
I know 90's cause A LOT of resistance.

I tried to google this but all I found was that using PVC piping is advised ?AGAINST? on the return line??

It causes less resistance to use flexible vinyl or silicone tubing?
Do most people use flexible vinyl tubing?

Appearance isn't really a big deal, the whole thing will be concealed.
So how do I determine the heading, and what material should I use??