Trey has the biggest draw, pretty simple. A not insignificant number of people will be there only because he's playing, to the chagrin of many old deadheads I'm sure.
The thing I don't like about John K is that he has no original licks of his own. Give me someone who will interpret the music in their own way: I like Phil & Friends way more than Furthur for this reason. Give me Kimock, Herring, Scofield, Derek Trucks... I'm not a Warren fan but he's a way better choice than John K to me. The April 1999 Phil & Friends shows with Kimock and Trey is probably my favorite post-Dead run of music - Trey isn't the player he was in 99, but I am interested to see what he does this time around.
Love what Joe Russo's Almost Dead is doing right now. The most enjoyable thing to me to listen to is a fresh take on timeless music. That to me is the spirit of the Grateful Dead, and Jerry more specifically. I understand people who only want to hear someone try to copy Jerry's licks and sounds ("who will play Jerry's licks" is a great line from that spoof video), and I get the argument for why that is what this specific event should be, but... we have the tapes for that, nobody does it like Jer. Give me some inspired improv that breathes life into an amazing catalog of songs.