Nihon_Ni wrote:
Asking others what watch you should buy is a bit like asking for advice on who you should marry, or if blondes are more attractive than burnettes. There are many beautiful (and ugly) watches, but your opinion is the only one that counts. I have a watch that I've worn nearly every day for 15 years, and it's something I love. Others don't like it or like other watches better, but that doesn't diminish my enjoyment of this watch.
If you're looking to buy an heirloom, I agree with the concern over a digital watch. I had been considering a B50 for a while, and for the very reason you highlighted I haven't purchased it.
You could certainly have one engraved. Perhaps your name would be more appropriate addition to a watch you intend to pass to a grandkid, but again, you get to decide what your heirloom is. The good news it this is a decision you can always decide years from now, and add the inscription once your have sat with the idea for a while.
My general advice to you is to not rush into this purchase. Picking a watch you'll wear every day for the rest of your life, especially one that will become a family heirloom, needs to be approached with great caution and consideration. Go visit your local AD often, read about different watches, and let the one that speaks to you bubble up to the top. I've found pictures of watches and watched videos of them, then went to the AD all excited about adding a watch to my rotation, only to be disappointed for one reason or another when I see a watch in person.
The watch you want not only tells time, it tells a story about you. Your grandson will wear it and think about you because the watch is a reflection of your personality and the days when he saw you wearing it.

Couldn't have put it better myself.

As Nihon_Ni rightly said, the absolute key point is don't rush any of it - don't rush the purchase and definitely don't rush the engraving, and mechanical over quartz is a must for any heirloom consideration.
All I would add is that I would tend to go for something iconic/classic - something that has already stood the test of time, and will therefore be likely to continue to stand the test of time. By that I don't necessarily mean vintage (although it's an option) - I mean something modern but with classic/iconic styling. Like a Navitimer for example. Some things that look cutting edge now may end up looking seriously dated in only a few years.
But that said, the choice is entirely yours, and YOU have to be happy with it first and foremost. What anyone else thinks is utterly irrelevant. It sounds like you're quite new to these type of watches, so (again as Nihon_Ni said) read up and learn about the different options out there before taking the plunge. Good luck!