my vote is with LC as well. i got their headers for my 99 2.7 and have been very pleased. everything is an exact bolt-on. absolutely no cutting or welding required. i have not heard the same for downey, but i don't know for sure.
Ive had Downey headers on my 3.4 for 100,000 miles and no problem so far. However I wouldnt say they were easy to install but I dont think that has to do with the brand. Remember to make sure to re-route the any electrical near the headers as it will melt them. Also save yourself some time and wrap the headers while your installing them, Ive gone through 3 clutch master cylinders as the headers emit so much heat it cooks the fluid in my clutch lines which run near the headers.