The double 65nm is older, which came out at the end of 2008, and the CPU and GPU both use the 65nm process, which completely solved the previous three red problem. But it is no longer produced, and you can only buy second-hand machines at present.
Dual 45nm also known as the XBOX360 SLIM, is 10 years out, smaller, more integrated, less power. Both the CPU and GPU use a 45nm process and are integrated into a single chip, adding support for WiFi 802.11n. The current new XBOX360 is this, but the latest version can not be cracked.
As far as personal understanding is concerned, it should be the double 65nm material with the most sufficient, the most stable operation, and the homemade machine can be turned on in seconds. The XBOX360 SLIM was modified to start slower and run hotter, but there were no problems.