I'm going to try all four titles, as I'm usually pretty open to trying new comics, but I have different opinions on whether I keep reading them:
1. JLA: Looks like a book I'll keep reading, due to its interesting cast interesting build up so far.
2. Threshold: Doesn't interest me too much, but I'll see when I pick it up.
3. Vibe: I know nothing about the character, so I'm basically going into this with a blank slate. I'll keep reading if it's good.
4. Katana: I've been burned twice by Nocenti twice now, and with one of my favorite characters (Green Arrow). This book will have to be really good to convince me to keep buying.