Which Speedmaster to get

Between the two you're looking at, my vote would be for the Speedmaster Pro. I personally prefer the two register Speedmaster chronographs, such as the Speedmaster 57 or Speedmaster Racing. I usually wear them on bracelet, but feel that they suit a variety of straps as well.

That white dial is lit 🔥🔥

OP, I think either choice is fantastic.  In terms of looks, I think the red gold on steel wins hands down.  However, depending on the use case, the 3861 may win out.

I would argue the following:

• If you plan to keep the watch forever and then hand it down as an heirloom, then go with the 3861.   The new co-axial movements are lifetime movements.  Omega incurred massive costs in rolling out the co-axial escapement throughout their entire catalogue, in order to address the primary failure mode in mechanical watches - oil degradation due to heat and friction in the escapement.  While they can't say so, the intention of the co-axial movement was to have an entirely service-free movement for the owner's lifetime
• If you buy watches, enjoy them for a while, and then sell them off again, I would say go for the red gold on steel, because it looks the absolute business and is a really stunning piece!

The red gold on steel looks amazing, is definitely more unique and stands out more. 

The all black one looks too flat in my opinion. 

The 57 is the stand out version for me. 

S&G day date would be my preference. I like to have a date if possible, and a bit of gold is great. It's also going to be a rarer piece, so is more likely to appreciate in value as it gets older. (The main drivers for vintage are brand, condition and rarity).

#speedmasterprofessional all the way for me! Classic design and history. Ultimate versatility! 

Agree with @HotWatchChick69 , the 3861 has one of Omegas better movements, the co-axials are great and interesting advances. I have an AT with the Sedna gold and it looks good on. The more traditional Speedmaster is a fun watch and an icon, but a somewhat dated design. 

You can’t go wrong with a Pro 3861

I vote: 3861 :D 

I know f-all about Speedmasters, but between those I prefer the classic Pro, purely for the register layout.  I think 369 looks better than 6912.

Thanks for sending me to the website though.  In your shoes, I'd have a hard time passing on the 39.7mm Sedna FOIS or the 2 tone Mark 2.

That said, I think you should get the z33, because it's awesome.

There are so many speedmasters that we can speek all day (week?) about them.

Let's make it short:

You cannot go wrong with a professional moonwatch, whatever generation.

For further questions like size, movement, hesalite or sapphire crystal, etc..., do your homework according to your needs.

Good hunt