There are 4 watches off the bat that fit your profile. The Explorer 1 the Onega rail master the datejust and the AT. Of those in have the 39 mm E1 and the AT Master coaxial. These are all perfect designs.
The AT is slightly less time tested but it is just amazing to wear ( I have the larger size. Look at my avatar ) it is still my favorite Omega watch and I have or have had a PO 45 mm 2500 a PO 8500 42 mm a speedy a PO LMLE and the AT. I can't think if any reason why to buy the older version instead of the master c. Not just because of the movement, but IMO the design is better and the proportions perfect. It is also a very sturdy workhorse that runs under any possible condition and at 150 M water resistance will serve you well anywhere.
The rail master and the E1 are somewhat more classic, enduring, bespoke jewels.
The datejust fits IMO on the same category as the AT with a slightly more dressy edge, but still simple design and doesn't try too hard. But the AT wins that one for me.
I recently took my AT and an SMPC to Mexico on vacation. I ended up wearing the AT most of the time.
Lastly, for me, blue.
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