I’ve had a Rolex Day-Date and (my current watch) an Omega Aqua Terra with month-date complication. There’s really no question: the day is far more useful for the reason mentioned. I love my current watch for a whole bunch of other reasons, but I’d never argue the point. I wish it had day of the week. (That said, it’s an annual calendar, which is an amazing complication.)
I also agree with the point made about value retention. If you’re buying at retail, you’re going to lose money on an Omega—there are only a few exceptions and most of those are not pieces that are readily available. If you buy preowned (which is what I’d suggest—just do your research and maybe post pictures here before buying), you can do better financially. But Omegas in particular and watches in general are not money-making propositions.
All that said, I think the Aqua Terra line is the best go-anywhere-do-anything watch, period. It looks at home with a tux; it looks good with shorts. You can swim with it. I dare say you can even mow the lawn while wearing one. And I’ve tried ‘em all, folks: there is no better bracelet on the market. It lacks microadjustment capabilities, but aside from that it’s ideal in every way.
I’m a strong buy on this watch. 😀