depends on the watch in question.
for their best/most favoured customers, rolex ADs can offer up to 25% discount for some of their full gold models (day-date, no diamonds).
hot models that are forever out-of-stock have no discount or may even be slapped with a premium.
popular rolex sports models have no to negligible discount (0-3% maybe).
don't look at the discount. look at watches that won't lose much depreciation on the secondary market. you may not be selling it. but it's good to know it can retain better than other brands.
a quote from a watch dealer featured in a show: "your watch is worth what you can go out and sell it for" is what i agree with.
i used to be a fan of the omega speedmaster professional moonwatch. i still like its look. i was fortunate to get my discountinued omega seamaster professional chronometer 2254.50 cult classic which i consider to be a superior choice instead at a good price.
read my review here.
no disrespect to moonwatch owners, but you should be aware that:
1. this is NOT an automatic watch, but a hand-winding watch.
2. it does not have COSC certification, thus after adjustment, it's variation cannot be guaranteed to keep to within +6/-4 s/day.
3. it's not hackable. so you can't stop its seconds hand to set the time accurate to the second.
4. it's water resistance is rated at 50m. don't you try swimming or even taking a shower with it.
if you're ok with such limitations, and you're happy to part with your money, go for it.
otherwise, i can humbly suggest that you save a while longer and get the rolex sub/sub-date instead.
1. it can do double duty as a dress and casual watch.
2. its brand recognition and pedigree is unquestionable.
3. it's value retention is highest among watch brands - include all the really atas brands with the exception of phenomena like philip dufour's simplicity, etc.
4. 5 yr warranty + 10 yr service interval tells you how confident rolex is with their engineering and QC.
just my humble sincere opinion. cheers!