The first omega (and "nice" watch) I bought was a Planet Ocean. I got the rubber strap with contrast orange stitching just because I liked it. Little color but not overwhelming, just looked at pictures for a while and kept coming back to that one. So I held out for a good grey market price and bought it when the opportunity arose. Three years later Chrono24 claims its worth $500 more than I paid, while I'm not sure that's actually true I think its safe to say its held value reasonably well.
Moonwatch would be a fairly default sort of recommendation for first Omega, but for me, I didn't want a manual wind and I wanted a date function. With an expanding watch collection worn in rotation I no longer find either of those things problematic, but for one I'd wear everyday I still would. You might not. There are some nice other speedmaster options that do have dates and auto movements though if those float your boat (I bought a broad arrow 1957 as my second watch which I do like but in retrospect knowing I wasn't going to stop at 2 watches probably would have gone with Speedy Pro).
Personally though, I've found the aqua terra is my most versatile watch and can take on very different looks with rubber, leather, or bracelet (buy it on bracelet the others can be more easily/inexpensively added after purchase) and is the best candidate for a one watch collection, but not so boring that you'd lose interest in it once you collect more. Side bonus is they are pretty reasonably priced too. Personally think that is a great place to start.
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