You want to buy a watch that will never expire and outlast you. To put it simple, you want the watch with the maximum level of longevity.
First, do not listen to the trends. You may think that this skeleton dial watch of some microbrand is cool and fashionable now. But how about 2050? It will not. So, buy a timeless product from reputable companies. This can be Rolex Submariner or Omega Speedmaster. Both models have already proved that they can last decades and will be relevant at least for another decade.
Second, do not underestimate the watch movement. Though quartz movement is easier to use and requires less maintenance, the mechanical watch movement is alive. It needs winding and servicing. Therefore, it creates a connection between owner and the product. The latter is not just an object of usage but an object of maintenance.
Third, the fact that you buy the heirloom means that you should not think about the brand of your watch. Your grandchildren will not be interested in your brand. They will be interested that you used this watch every day during your life. Therefore, try to buy a watch that you will enjoy wearing. Otherwise, luxury item will become a paperweight.
As far as the price of the watch is concerned, of course, the price is important. But, of course, you should not spend more money than you can. There are many watches that are reliable and beautiful and have different prices. Maybe, Tudor Black Bay suits you. Or even plain but elegant Seiko Presage. All these products are robust enough and have soul.
Fourth, maintenance is important for the mechanical watch but nobody talks about it. Every five to ten years, your watch needs maintenance procedure for a couple of hundreds of dollars. Think of it as changing oil in your car. If you skip this procedure, you will have to repair your watch movement which costs a lot of money.
Moreover, you should consider the size of your wrist. Even though 42mm in diameter is perfect for the showcase, it looks not so good on a slim wrist. Try it on yourself and see if the lugs do not hang over your wrists. Comfort is the main thing to consider since you will wear this watch decades long.
Fifth, the material of your watch case is also very important. Steel is the most robust metal but scratches easy. This makes your watch unique and beautiful. Gold is softer and wears faster. Titanium is light and robust but has its special feel. However, for the real heirloom, steel would be the best choice.
Lastly, remember to buy your watch from the trusted seller. The grey market has some discounts but they cannot provide warranty to you. On the contrary, purchasing your watch in the authorized dealer will give you the piece of paper which is an important part of your watch legacy.
Now you can go and find your future heirloom watch. Wear it and wind it up. Listen to that ticking. This is not only a watch – this is your future artifact.