HFC are a low end budget company. You can't really expect much out of any of their guns. Many tend to be problematic. But they do have some models that are better than others. Their M11 machine pistol GBB is actually quite good, as is their Mauser Broomhandle. Their Glock seems to be not bad either, plus it's TM compatible, so parts are readily available. But I'd just avoid them over something better.
And yes, KSC make excellent guns all around. My KSC Glock 17 is the most badass pistol I've shot to date. Anyone who's shot it or been on the receiving end knows it can outrange some AEGs on the field. It's a crazy accurate gun with excellent range, and all stock internally except for a tightbore barrel.