Per this link: http://www.atariage.com/2600/archives/consoles.html they describe the first year the Atari 2600 Heavy Sixer that came out in 1977. They say the following:
This is the original 1977 Atari Video Computer System, and this particular design was only produced for one year. Because it features six chrome-like switches and has heavy internal RF Shielding, some collectors refer to this as a "Heavy Sixer". At first glance it looks just like the CX2600 that follows in 1978, but it is noticably heavier when compared, and has some extra plastic molding around the back and sides of the unit. These units were manufactured in Sunnyvale, California, and there is a tag on the underside from the manufacturing plant to indicate this. There is also a serial number on the unit itself with a matching serial number sticker on the box. The later model was manufactured in Hong Kong.
Thus, why I am asking about which Heavy Sixer is more rare or valuable, a Heavy Sixer manufactured in Sunnyvale, CA or a Heavy Sixer manufactured in Taiwan, is because I have a chance to buy a Heavy Sixer made in Taiwan, and I want to see if it is more valuable than a Heavy Sixer manufactured in Sunnyvale, CA.