I'll give my opinions on all of the options.
Detonator: I've been on this only once, but I loved it. The drop was very forceful, but it would have been even better if I got on it with the old countdown
Rush: Really boring.
Maelstrom: It's quite good for a swinging ride type... my 2nd favourite swinging ride in UK theme parks, but in general it's just average.
Apocalypse: I absolutely love this ride. It never gets old... ever. It's amazing.
Vortex: I've done much better, basically.
Cliffhanger: I've only been on it on shot mode only, so it wasn't the best. I bet it's cool with shot&drop, though.
Hex: I'd call this a dark ride to be honest, not a flat. I love hex to be quick.
The Haunting: Probably the most fun ride I've ever been on. I love it.
Slammer: Slammer's very cool. I really like it a lot.
Samurai: Definately one of the worse flats I've ever been on. So boring and embarrassing.
So, overall I'd put Apocalypse at the top from the provided list!