Serial card

I’m trying to determine the best digi card to use with my IPower 9000:

Digi AccelePort Xr 920
Digi AccelePort Xp
Byterunner Cards
Digi Edgeport Serial Converters
DIGI PortServer TS

Any input is welcomed.

Some things that might help to give you a recommendation:

What OS do you plan on using the serial solution with?
How far away from the server will the serial devices be located?
What type of serial devices will you be connecting?
What sort of traffic will be going over the serial ports?
Is the data going over the serial ports timing sensitive?