Definitly DO NOT fit triples onto a carrera banshee frame, Ive seen one snap with my own eyes because it had junior t's on.
They are not designed to take them (triples put massive tension forces along the top of the top tube). The tubing is quite thin in the top tube.
Pretty much any single crowns hould be fine though.
Hehe, i had junior t's on my carrera banshee

(never broke im glad to say)