Hi
Yes, generally the longer a name has been registered the better. However it obviously depends on the quality of the name. Generally better names are registered first and therefore have been registered longer, however there are exceptions and a name that has been registered for a shorter period of time may well be better.
As far as the amount of time left on a registration it matters when dealing with small value names. If you are buying a name for $10 and it expires in a weeks time it means that you will really have to pay at least $17 for it ($10 purchase + $7 renewal fee). Therefore you may be able to find a better quality name for $15 that has a years registration left on it and have yourself a better deal. However when dealing with large value names it really doesn't matter.