I have all three plus granulosus. The Niger are without the best when near adult. My largest looks amazing swimming around and hoovering up his food. He gets on well with all including a 18" giraffe and another Niger. Granulosus and irwini are so slow growing (IMO & experience) anyway. I have photos on the catfish threads of both, one with the Niger and Giraffe together.
I'd go with the Giraffe, friendly, inquisitive, non aggressive and not piscivorous. Although they may grow a little large. Irwini are cool buit do nothing all day and not much at night
