The Haunted House definitely takes my vote (If there was a poll then it's exactly what I would've chosen) rather than Duel.
[youtube]http://www.youtube.com/watch?v=Z7tn3QIK8Wk[/youtube]
The Haunted House had so much more to the ride because it was meant to scare you, it was meant to be a little cheesy with Hammer Horror like effects but never to a funfair standard and it was meant to be an immersive experience overall. That was the point. I never got to experience the original, the most I can do is see old POVs and promotional material (All of which send a little dark ride shiver down my spine) because that kind of well thought and well crafted ride, much like other dark gems at then Tussauds parks, will never truly exist anymore. It was a ride of the 90s that was replaced too soon.
Duel merely exists for the sake of the guns, it was a surefire way of making more people interested in the ride and getting them through the Entrance Hall. Not that I'm saying the entire place would be ripped down if that option was ever given, Wardley forbid! It doesn't help that Duel's guns essentially nil the point of the ride either as the ride is quite rightly meant to scare you but because you're concentrating so much on little targets than the theming aesthetics, you're not getting the correct experience. It's the same for Tomb Blaster at Chessington; So many unique touches yet you're more interested in a greater score than your fellow visitors.
I'm glad however that the original SFX and music is slowly coming back to the ride, bringing it back to the glory days essentially and reversing the money making damage by late Tussauds.