It certainly is a very personal choice, and there is no 'correct' answer. Ive enjoyed reading everyones diverse opinions on the topic and I certainly learnt something.
For me when it comes to jewellery, I look for a design I like and quality of craftsmanship. I also like to know what the after sales service is like (free cleaning, support if there is a problem, if its a watch what kind of servicing etc). I usually lean towards buying 'branded' jewellery for one reason: I bought a local jewellers piece and a few years later I went travelling, when I came back the store was closed down and I needed to get some items repaired. Normally they would have repaired it for free since it was a flaw in their design, but I had to pay else where. It irked me quite a bit.
I have had a problem with a Tiffany & CO piece before and I got a brand new one years after the sale was made (and I mean a number of years it certainly wasn't new). That for me is what is most important.
I still purchase items I like from local jewellers and I have since found a jeweller who does custom pieces for me. However, I would say I go for items which are either massively too expensive from the branded stores, are something unique or I'm having an item repurposed/remade into something else.
Thanks for letting me share xx