If you look at things like the terminators at the start of T2, or the bad thing in Robocop (is it ed 209?) and like people in suits like in Aliens...
then compare them to CGI equivalents, they always win, don't they? They don't look dated at all. I know Robocop used a bit of old fashioned CGI in parts when he's fighting it, but still.
Another good example is Star Wars. The old ones haven't dated very badly at all. The odd thing is laughable, but on the whole, people in suits / animatronics seem to look very believeable. Looking at Episode I nowadays, after less than a decade, it looks dated.
Because CGI is always improving, I think it'll date much faster than animatronics. This is a shame for things like Lord of the Rings. When you watched it at the cinema, it was breathtaking, but at this rate, will it end up looking like Willow in years to come?