Here are your main options:
old qu-ax £175.00
Even though the old qu-ax is cheap I would avoid it because well it’s cheap. It has a heavy steel rim. You would want to upgrade the seat and pedals, and may possibly want to invest in a T7 handle. 22.2mm seat post, bit small but ok.
new qu-ax £263.00
Very good cycle for the price. Light, strong wheel. Again seat and pedals need upgrading. A big positive for the new qu-ax is its isis hub. It makes for a very reliable crank/hub interface even after many many crank changes. This cycle also comes with a cheaper but still good brake. Again you may want to get a T7. Comes with a 25.4mm seat post, better.
Downside - isis cranks cost extra, and there is enough but not as much of a range in lengths.
Nimbus 36" £330.00
Very nice ride indeed. The standard model is £295.00, thats with a steel rim. With the upgrade to the much needed better rim, in this case the Airfoil rim, it comes to £330.00. It Comes with better pedals, you may want to upgrade them to something even nicer when you get serious but these will last many hundreds of km. Good seat. Have the option of upgrading to the T7 for £5 cheaper than if you purchased it seperatly. 25.4mm seat post.
The nimbus frame is stiffer than the two qu-ax frames. And also gives you the option of running magura brakes.
Nimbus 36" Nightrider Pro RTL £395.00
The ultamate ride. Nice frame, nice rim, and in my opinion nice colour Comes standard with the T7. The only one of the four that has the new Nightrider tyre, the rest have the smooth TA tyre.
25.4mm seat posts are easlier to find in bike shops than 22.2mm. If you get the T7 and ride seriously, you may want to find something other than the KH post. The joint between the post and the ‘head’ isn’t the strongest. Mines starting to give me issues.
The qu-ax’s have regular width hubs and the nimbus’s (nimbi?) have extra-wide hubs. Extra-wide hubs make a stronger wheel but give you more wobble when riding. The new qu-ax is 48 spoke making up for the weakness of a narrow hub.
I have the new qu-ax. I upgraded the seat and pedals to a KH freeride and snafus. Later I also invested in a T7.
145mm/152mm are a good starter crank length for 36’s. I started at 170’s because the thought of no control scared me, but within a couple months changed down to 125’s and never looked back. Sure they are little harder to mount with, but with practice you have just as much control.
It depends on how much money you have and how serious you think you will be about distance riding, and maybe how much you like purple Personally I would avoid the old qu-ax, and the blue nimbus without the rim upgrade.