Comment by da_chicken

It's mostly down to preferences and needs.

DBeaver requires Java, supports more RDBMSs, supports plug-ins, supports ER diagrams, but is also a project split into a community/enterprise model so some features are just never going to be implemented or improved upon without you paying an annual fee.

HeidiSQL is written in Delphi, supports the major RDBMSs (except Oracle), and is more focused on being a query analyzer than anything else. There is no edition split or paid model, so you're more likely to see new features in the free edition.

IMX, HeidiSQL is faster. It loads quickly and performs better, though I will say that my experience with both is about 10 years old at this point. From my memory, the DBeaver interface has always felt clunky in that way unique to Java applications, and many of the features in DBeaver are things I never wanted or needed. At the time, HeidiSQL was Windows-exclusive, with Linux support only about a year or two old at this point. My opinion 10 years back was that I would use HeidiSQL when I could and DBeaver if I had to.