What's so good about ANY brand name product?
For me they fit and feel the most comfortable in my hands. That translates to being more likely to place my shots where I want them more "naturally" than having to train harder with something that doesn't fit so "naturally". I learned that through personal experience over 20 years of shooting handguns. I don't buy hype and marketting.
I also prefer the lack of an external safety as the internal mechanisms designed and employed in the classic SiG SA/DA action just makes more sense to me and removes at least one step from "draw to bang" compared to a 1911 or BHP for instance.
I find the asthetics of the SiG's appealing, personally. Asthetics are subjective criteria anyway so what one person finds attractive another may not and there is nothing wrong with personal preferrence. Functional, simple and without a multitude of protuberances to potentially catch and snag upon when one has to draw. Purpose built and rugged in design.
Asthetics aside, most people that like Glocks don't like SiG and vica versa. The primary reason for this is the grip to slide angle present in the frame. Adding back to the comfort mentioned earlier, The Glocks just do not feel right nor good in my hands. Don't get me started on the trigger safety thing either.
Basically it comes down to "different strokes for different folks". What works for one person may not for another and that is why I always advocate "test driving" if at all possible or at least getting as many in your hands before buying over just buying by brqand name or hype. Glocks are fine weapons as are Beretta's and so on, but I don't own any of them anymore. That said, I buy what works best for me, your decision making process may differ from mine.
Firearms are nothing more than tools when you break it down. Go ask a charpenter or framer which brand hammer they prefer. They will be specific to their needs and preferences as well as what fits most comfortably for them over brand hype, I'm willing to bet.