There will always be much debate over this, but I agree with you, beechan.
Yes, we cannot really say whether Judas was an unregenerate 'devil' or unbeliever, either before or after he betrayed Jesus. We really have nothing given to us anywhere in the Bible to say one way or the other about whether he was a believer or not. Even in John 6:64 or John 6:70. And like you say, he was chosen and called by Jesus, just like the other twelve... Matthias was eventually chosen to replace Judas... disciples/apostles. It's a valid point that there is no explicit repentance by Judas, but this is the case with several characters in the Bible, and there's also nothing that suggests he was not penitant. By the same token, there is never any explicit repentance made by Peter for denying Jesus. But Jesus says to all of them in John 15:16 ~ and Judas was present ~ "You did not choose me, but I chose you and appointed you that you should go and bear fruit and that your fruit should abide."
Again, this has been and will remain a debatable topic, and to be honest I have struggled with it within myself, but yes, I think Judas will be standing with us on Jesus's right in the final Judgment. <smile> But, you know, whether I am or anyone else is right or wrong about that doesn't really matter, does it? <smile>
Grace and peace to all.