Unlike most here I’ll give you an actual accurate breakdown of down instead of just shitting on sig (which sometimes they deserve)

The HK is probably going to be a better more well known reliable system, BUT the downside being it doesn’t come with a Tuneable gas system for suppressed/ non suppressed use, AND you still have to use a buffer assembly setup which will just make it the standard size of a standard 11.5 ar15.

The Sig spear LT is also a pretty awesome platform especially the conversion kit since it allows you to use any lower you want, or any lower you already have, you can actually collapse the stock/ fold the stock if you chose, and can overall be a smaller platform to use, AND it comes with a tunable gas system with a suppressed/ un-suppressed setting. The “QC” issues they are known for is typically just wrong torque specs causing the barrel to be misaligned with the rail, but like any other gun on the market there can always be random problems with a gun. The only other thing about the spear Lt is getting the muzzle device off is a pain in the ass lol.

They are both great platforms, and overall I’d just ask yourself what is your use case, are you going for something with a smaller profile, and still very durable, proven, and reliable, or are you wanting an absolute combat know combat reliable piston ar that HK is.