Welcome, that list sounds like classic history to becoming an Aero owner.
My thoughts.
The Max still remains #1 for me due to the style as it is pure art. They made a 100 so it is limited edition. It is a little older than the coupe/SS but if well maintained there should not be a gap in the experience.
The Coupe/SS were not limited edition but did not sell as well and so there are probably actually less of them. As Gajet mentions something around 16 Coupes was a number I heard. Slightly more SS I think. Now both are generally out of sight and the company is focusing on the Series 5. Mine is on the video here
https://www.youtube.com/watch?v=OR6lwpfte9Q. When the good lady wife saw this video she just said "Yes". Actually she paid 25% of it.
Have you not considered spec'ing a new Series 5 of your own? You are in the right place money wise and the pictures don't do it justice. The fun of ordering, spec'ing and seeing it built at the factory is not to be underestimated. You don't mention if you have been to the factory yet, you should.
In essence the differences I note through Max/Coupe/SS.
The Coupe/SS had more development time as it came later and so has some advances. The boot is large and surprisingly practical. I collected my US CEO from Heathrow in the Coupe and his full size carry-on luggage and coat/computer slipped carefully straight in. Once he had stopped gawping at it he laughed at the reaction it was getting all the way to the office. It is not quite as pure and beautiful as a Max but it still creates zombies everywhere it goes as they gawp mouth open.
If you like loud then the dual sidepipe often found on the Coupe/SS are going to be an instant deal maker. Its nuts, good nuts. They can be fitted to earlier cars. Several of the AeroMax had single sidepipes and this was actually a good compromise on drone vs noise. Medium-mild volume around town but wicked on full throttle and higher revs. The quad rear are the most comfortable but still great sounding, just less so inside the car. If you have a Larini on the other cars you want the dual side option. You really want it. Its better, soooo deep.
Coupe or SS ? Like Gadget I bought the factory Coupe when it came up for sale thanks to a kind member of the board helping. It needed a fair amount of tweaking but it is in the garage and not budging. I went with the Coupe because my intention was to use it heavily and I had heard comments on the squeaks and possible rain ingress on the SS panels. I also quite like the single colour effect of the Coupe shape as it is a little gangster-rocketsled. Downside - there is a fair bit of resonance and NVH in the cabin as it is a tight metallic drum. When you add sidepipes to this then long runs are best done with earplugs. It creaks as well. I do care but not enough to offset the grin.
The SS open roof does give the car another dynamic. We retained our first Morgan - an Aero Series 2 - as the Coupe had such a different feel about it and an SS with removable roof might actually be best-of-both to a degree. As we had retained the S2 the more useful nature of the Coupe (especially the ex-factory Geneva one we had in this colour) was different enough to justify keeping them both using man-maths.
I feel a little embarrassed about having two Aeros, for many it does appear flash but the S2 has gone up modestly, better than bank rates. The Coupe and SS do not get Max prices today but over time I think they will all converge with the Max retaining some premium due to its beauty. At the end of the day the Coupe/SS is ironically more rare than the Max!
They will all need some tweaking, they do all creak a bit. Rock solid platform but the bits wriggle around and need sorting. Never stops it working. Its all down to knowing who looked after it before and getting an experienced engineer to look over it before you buy it, even if it is from a dealer.
This forum also adds a lot of value to being an owner and is far more useful than other boards I use through previous cars. The Morgan community is actually way ahead of other groups in my experience.
I bought the Coupe to use every day. I did not end up doing that as we needed a large boot for other reasons in the end. I then bought an E63S AMG Estate and have just replaced it with an RS6 Performance. Yet when I had to go to Paris a few weeks ago I took the Coupe. The RS is a blunt but deadly tool, I am not enjoying it. Last year I did 9000 miles in the Coupe and 3000 or so in the Series 2 with a trip to our old HQ in Hilversum being a good part of it. They are surprisingly easy to drive and comfy on longer journies. The effect it had on the business partner I was meeting in Paris was to get the CIO to move his car out of his reserved slot and place the Coupe in it for all to see in front of their building. I did not ask for anything, they said it was so beautiful that they wanted it.
They get under your skin. Just don't forget to use it, lots. Go to the factory, think about a Series 5. Drive a dual sidepipe car. Push the button.
said it was her favourite too, with an SS second, and the S3 third. 
