Both of those bikes look like they would be a lot of fun - I can see where you might have a hard time choosing between them.
From the Ariel web site it looks like the Model D is currently back ordered, and now only comes in the 'premium' configuration with the front suspension fork and the 18 Ah battery? Have you contacted them to determine whether their May 25 availability date is still accurate after this year's earlier China shut-down?
One immediate thought I had is whether I would want the extra weight and complexity of having the 2 motors which the Ariel has. Obviously it would be great if a lot of your riding is going to be on really loose surfaces (snow, sand, etc.), but it doesn't sound like that is your intended use for it. "Light off road" should be easily handled by a single hub motor.
Luna stuff always leaves a lingering question in my mind - since you have to pay for any reasonable warranty (looks like you get one year with the Ariel). On the other hand I have heard more good stuff than bad about Luna, and there is no doubt that they have excellent battery design and building skills. But their basic battery on the Banana is already lower in capacity as compared to the Ariel, and their base price is already higher.
From a purely cosmetic perspective, I like the Ariel better. And its seat looks way more comfortable (although appearances can be deceiving).
From the 2 you have specified, I would probably go with the Ariel D if it will be available in a reasonable time frame.
Any reason you don't have the Super73 or Juiced Scorpions in the running? I think that the new Super73-S2 is going to be a heck of a bike - I'm really not sure that full suspension is necessary on these types of bikes with their fat tires. But if it is something you really want, the Super73-R's will have that.
Regarding the Juiced Scorpions, well I do have one of those (HyperScorpion) pre-ordered for my wife, but now we are going to have to wait until July to get it, as opposed to the original May availability date. Oh well.
Good luck in your choosing, and have fun!