Well thanks guys! I can't help being struck by the fact that, despite my request in the OP, so many posters couldn't resist insisting that it was just a matter of opinion. Couldn't people disagree about THAT? You might say its all about personal taste, and I might say its not about personal taste at all, its about, materials, engineering, efficiency, reliability and design etc. etc. Would that mean that whether or not such things are just matters of opinion, would be a matter of opinion?
It seems obvious to me that questions about how well engineered, well designed and well finished a given watch is, AND questions (though this is perhaps more controversial) about how original and stylish it is, though they may be hard to settle, are questions about what is objectively the case, not questions about how things seem to this or that person. If you insist that such questions are matters of personal opinion it immediately follows that there could be nothing for us to disagree about - no point whatever in giving reasons to think one thing rather than another. If 'Rolex is better than Omega' just means 'I like Rolex better than Omega' then none of us could ever be in a position to disagree about THAT - after all you know what you feel better than I do - but then we'd have absolutely nothing to talk about! All we could do would be to inform others about which feelings we happened to have - and why should I be interested in that?
If you have ten times more disposable income than me, you will be able to think seriously about getting wathces I had better not think about at all. On my income I'd better not start wanting a PP, but things may be different for you. But that doesn't mean we couldn't give a series of reasons for the view that PP are a better watchmaker than say Rolex or Omega. I can just say something like - well if I had the money I would prefer this watch to that one for these reasons etc. etc.
Whether a judgement is subjective depends on what its a judgement about, not on the fact that some particular person has made it. (There are no judgements that no particular person has made.) So just because its me rather than you that is making a particular statement doesn't mean that I'm just stating my personal opinion.
It seems obvious to me that horology is a genuine craft which combines engineering and art in something like the way that architecture or cabinet making does. So people can make mistakes about what has horological value - just because someone thinks a watch is good doesn't mean it is. That means we can have reasonable debates about which watches are better than others (etc.) and those debates are not about how each of us happens to feel.
Even judgements about what is ugly and what is beautiful are hard to think of as mere expressions of personal preference. Downtown Detroit is uglier than downtown Amsterdam - and if you disagree with that there's something wrong with your aesthetic sense; Mozart's Requiem Mass is more beautiful than Paul Simon's Graceland album; Angelina Jolie is more beautiful than that woman I saw stuffing meat into her mouth at McD's yesterday... The idea that beauty is in the eye of the beholder has always struck me as crazy - just because I like something, it doesn't mean its good - I MIGHT BE WRONG. (When I first heard Charlie Parker and Stravinsky I didn't like them - I have since learned that I was missing something). The fact that people disagree about what is beautiful doesn't mean that there's not such thing as genuine beauty.
People don't want to come across as arrogant or conceited or know it all - so if you're friend tells you he's fallen in love with a Russian diver by Invicta you (because you don't want to be a jerk) start talking about how its all a matter of personal taste and how he should just get what he likes. The fact is that he should come to realize that there are other watches which are a bit like his beloved Russian diver, but which aren't so go damn tasteless. You might show him some and point out to him the differences, and he might start to cotton on. If he did, he might look at the bling-bling watch he liked yesterday and realise his mistake. That sort of thing happens all time - once I listended to Queen all the time, now I listen to Bach and Charlie Parker - once I ate corn-dogs all the time now I eat salmon and spinach - but its a brave man that tells his friend that he's crazy to like this or that because it lacks all aesthetic value...
Of course I'm not worried about coming across as arrogant and conceited...
I don't have a clue what the best three wathmakers are because I know SO LITTLE about watches - I'm going to go away and research the companies you experts have recommended. I cautiously suggest that the most original design I've seen amongst dive watches - which are the kind of watch I like best because they are both elegant and sporty - is the Seiko Black Monster.