I have to admit I absolutely adore all 3, but my vote has to go to the National. Its the better of the 3 by some distance, and it was my first coaster besides the Little Dipper what got my hooked on coasters.
The RollerCoaster, I never really rated as a child, I always found it tame, however as I got older I appreciated it and its history a lot more, and during the busy 50p weekends it was always the ride you were guaranteed to be able to get on quickly due to it having such a high throughput back then. Along came the ex Dipper train with lapbars, and boom, it found a new lease of life. I thought they would ruin the ride by putting lap bars on, infact the heavier train made the thing so much better.
The Dipper has always been somewhat overshadowed by the National, it doesn't do anything wrong but it simply isn't the National. At almost any other park it would be my favourite coaster, but here its not quite good enough.
That said, the Nash is in serious need of some love. Its a shadow of its former self, it hasn't been right since 2006 when the new trains went on but its certainly getting a lot worse now.
GCI need to redo the entire layout, and new trains need to sourced with more suitable lapbars. Along with that the station needs reworking to make 4 train operation something other than a pointless activity.
Anyone who rode it before the 2004 fire will know how much airtime it can deliver, the first drop didn't require you to brace yourself, the second double was a reason to laugh and everyone came back to the station smiling often re-riding. These days you often see people holding their back, walking like they messed themselves, and staggering off elsewhere. It really needs to be put ride, its the one ride in the park that doesn't just need a few million spending on it, it actually deserves it. For around 60 years its been the signature ride at the park, and its got some many enthusiasts into coasters, to see it referred to as 'sh*t' is actually upsetting.