Vintage Datejust help

[City74]

After a few years of watch collecting, mainly affordable brands (Hamilton, Seiko, Damasko etc) and having bought and sold roughly 50 watches, I have finally been narrowing down my collection to 6 must have pieces. One of those pieces is a vintage Rolex Datejust.

However after reading the do’s and don’t of buying used I still am left with a few questions and thought this would be the perfect place to ask.

I’m looking to add a 1601, 1603, 16200 or 16030. Here are my questions...

1). Are there certain years or models within the Datejust line that are more prone to issues or are known to have issues more than other years? For instance was there a certain couple of years that Rolex changed something that didn’t work out just right? Maybe a movement or crystal etc etc

2). Is there a model or date (dates) I should look for in particular that is a “better” era of watches?

3). Lastly if the price is roughly the same whether buying a 1601 or 16200, which era watch would be the best buy and why?

Thanks in advance for any help

PS...I already know to buy used from a reputable dealer and I have 2-3 in mind that I would buy from.