Karen - you're asking the wrong person. xD I'D SAY GET THEM ALL. LOL. but maybe if you can find a link of a concert, you should watch it? or watch snips of it on YouTube, lol.
but my favorite 2 are: TOUR 2007 cartoon KAT-TUN II You && KAT-TUN Live Kaizokuban.
kaori - of course! PM me as usual~!