Buy what makes you happy, there are plenty of nice watches at every price point. I have a few affordables, a few luxury watches, and most of my watches in between. Right now my favorite is my Hanhart, tomorrow it might be my Oris Aquis, or my Seiko or Orient.
If anti-magnetic properties are important to you then go with the 39 if you want a see-through case back but antimagnetic properties are not important then go with the 42mm.
I am not a fan of heavy watches, I have an Omega Seamaster pro-Chrono, and I rarely wear it because it weighs my wrist down. I think this is the reason why I always steered away from Chronographs because of their size and weight.
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