I've done Helvellyn via the Great Dodds and then down the Dolly Waggon; I've done Snowdon coming down Llanberis, The Rangers and the Rhyd Ddu and; I've also done the Llanberis twice in one day with the Llanberis and Rangers descents (yesterday) so....
Snowdon is certainly NOT a bucket list route to do. The climb up the Llanberis is a challenge. The gradient isn't that steep but it's relentless and if you push yourself two thirds of it are ridable and a test of technical climbing skills, but hey, who sets the rules that say you can't push all the way up if that's you want to do (not me) ?
Llanberis down is a fast flowing blast and it's rideable all the way down apart from the first steps off the summit. It's a just reward for anyone who has climbed to the top.
The Rangers path is comparable to the Dolly Waggon descent. I would say it's better though because it's more natural. This year more of it has washed away and some of the drops and switchbacks take some real skill and guts to do. The Dolly Waggon is rideable all the way down and a tad easier.
The Rhy Ddu is hard work. The first section is un ridable, the second section is no good for anyone who's afraid of heights (a walk along a cliff hugging foot wide rabbit trail (with a bike in your hands while the wind batters you)), the third section is like a moonscape and the rest is just large slabs and mud. It used to be an area of mine workings by all accounts and it shows - I didn't enjoy it and it's knackering, plus the climb from the road to go back over Maesgwyn to the start of Llanberis is effort enough to put you off going back up to the summit (but not in Scareys case !).
Doing Llanberis up and down or Llanberis and Rangers is not enough for me, you've climbed for and hour and 45 mins and you're down in less than half an hour (15 mins if it's Llanberis). The double is a challenge worth doing but not with Rhyd Ddu (Scarey Carey will probably die of exhaustion later on today when he realises what he's done !). Both times I've done it I've suffered with cramp coming down the Rangers (any suggestion to overcome this are welcome - I drank 2.5 litres during and a litre before I started this time and still suffered).
I think Helvellyn is great. The Dolly wagon is a good technical descent but I did feel like I could do some more when I got back to the car park even though the route is a lot longer than Snowdon up and down.
Both Snowdon and Helvellyn do something that the long muddy trails elsewhere don't. They provide a sense of achievement and a grin from ear to ear and they leave me on a natural high. I think that's why I always feel like I could go on and do more at the end. The difference is on Snowdon is that you can do more by simply turning round at the bottom gate !