For a MP5 clone the ones coming in from Pakistani Ordnance Factory are HK spec and ready to go. They come in as a pistol so they are ready to convert to a SBR or add a pistol brace to.

For a G3 I would go with PTR. They are well-built, reliable, built on licensed HK equipment, and can be had for under $1000. I would get the GI model since it has the deeper flutes in the chamber meaning it will be able to eat any ammo you throw at it. I used to have one but sold it to my friend because he really wanted it and I upgraded to a Vector. The fact that the Vector had the paddle release was a major factor in me getting it.