Either drive is probably as good as the other. The 6gb/sec doesn't matter at all --> sure it will make reading/writing the on-drive memory buffer (aka. "cache") faster, but you'll never be able to see/measure it in real life.

The drives themselves are maxed out over a 1.5gb/sec SATA-1 link, so no need to go all googley-eyed over 6gb/sec for mechanical media.

The 6gb/sec SATA link is being brought out for SSDs, which actually do need it to achieve maximum speeds.

As for the drives, dunno. All I have here are 2TB and 1.5TB Green drives, still working well.

Cheers