Which A-5 12 gauge barrel is more valuable, made in Japan or made in Belgium?

From a collectors point of view it would be from Belgium, from a shooter/hunter a Jap with choke system
A few years back the Belgium guns where demanding a higher price but that has changed.
With the advent of steel shot and the probability that non toxic shot will be mandatory the jap choked system barrel will be of higher demand therefor higher price

It has a lot to do with the gauge and choke also.
16 gauge demanding the highest price, no matter the country is was made in.

Go to barrelexchange.com and they will give you a good idea what the going rate is.