I read a guide at iclarified, they selected the custom firmware and not the original restore firmware in order to pwned the iphone.

After that they did a restore with the custom firmware using Itunes.

In the previous version of winpwn you used the original restore firmware in order to pwned the iphone, so i'm getting a little bit confused here:

I know you sholuld use the original restore FW to build the custom ispw, but to pwne he iphone should i select the custom firmware?

I ask this question because i have 3 iphones to jalibreak and don't want to build a custom ispw 3 times

The custom ipsw must be used only when restoring in iTunes.

From the xpwn readme, it says:

So I used the custom in pwning iTunes and it worked.

Clarification: I used the vanilla ipsw in step 4 of iclarified. I used the custom ipsw in steps 12 and 15

OK,

So should I iuse custom to pwning or original restore?

This seems to answer the OP's quesiton...
Use the custom only when restoring in iTunes, so go into iTunes hold shift and then click restore -- browse to your custom firmware -- and restore with it. I know i'm probably late posting this but maybe you didn't get around to it yet:p