I'll have a crack at this...
So first, it's always helpful in a post like this to include images of the watches in question. A quick note to disclose: I am an incredibly biased owner of the present Hesalite Moonwatch.
First up... the classic Moonwatch:
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Why you'd want this?
The history behind it is a major reason many choose this watch, but there are lots of things to like.
Rock solid, reliable movement (not chronometer certified, mind you... mine runs 8 secs fast per day). Unparalleled legibility. The ultimate strap watch (seriously, it looks incredible with almost any strap you can throw at it).
Also, many love the way Hesalite adds character to the watch... the way it distorts light when viewed at an angle. Hesalite, while easily scratched, can be buffed out to brand new with about five minutes of your time and some Polywatch. Also, if it ever was damaged beyond repair, a replacement crystal will run you less than $100.
Finally, at 42mm. but being relatively short lug to lug, it wears very nicely on a variety of wrist sizes.
Oh, and it's the cheapest of your stated options.
Next up... the current Moonwatch with a sapphire crystal:
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Look familiar??? Yep... Omega's website photos make this one look just like the Hesalite version. Thing is, in the metal the overall look is altered by the sapphire crystal.
There is a milky ring created by the sapphire around the inside of the tach bezel. Once I saw it, I was never able to unsee it and it's not something that appeals to me.
Pros are this one comes with an exhibition caseback so you can gaze longingly for hours on end at the gloriously finished variant of the 1861 (is it 1863?).
Because the sapphire front is better at transmitting light, the experience of admiring the dial is quite different. To my eyes, the dial looks a much deeper black... it's really nice.
Sapphire is nearly resistant to scratches, so that's nice, but is susceptible to cracking, which is both not nice and very expensive - like in the $1000 (?) or more range, I believe.
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Next up is the Speedy Pro Moonphase.
Same 42mm case width...
Like you, I love a good moonphase. This one is particularly lovely... I really like the colour of the blue sky.
The thing for me about this variant is the placement of the "Speedmaster Professional" text. It looks awkward to me (two fonts, weird positioning on the dial) and I can't get over that so, on to the next...
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This is a very very cool watch. No doubt about it. The little touches of red on the dial. No issues with text placement. Kind of a perfect design, really.
The issues to consider are:
It's a large watch... 44.25mm and it wears tall because of the automatic movement. You need a decent sized wrist - like 7" or above - to pull this one off. It's large enough that I think the size reduces the appeal of wearing it with a suit. My opinion... actual owners may beg to differ.
Sapphire crystal. Not sure if the milky ring rears its (subjectively) ugly head with this one.
The movement is apparently amazing.
One thing though... it's damned expensive. Like, you could buy a Tudor Black Bay to go along with your Hesalite Speedy for the price of this one!
So there you have it. Four guesses which one I'd buy
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