I wouldn't say one of his best. He still fought well but the fight was notable for Ruben fighting above and beyond himself to make it a tight contest, before the sure-fire late run by Ken saw him pull safely ahead.
From what I've seen I'd say his second fight with Laguna and his fight with Donato Paduano. He looked good against Carlos Hernandez and Carlos Ortiz too, but they weren't offering much resistance. I've heard he looked good against Frankie Otero and Al Ford too, but I haven't seen either. I do have the Otero fight in my collection and I'll give it a look some day soon and report back to you what I make of it if it is a good performance.
I think Buchanan was fairly consistent with his performances, barring the Watt fight where he was relatively poor.
