In our experience most drives on the market have been mediocre. If anything, the quality of the drives seems to be declining slightly this year. We have seen quite a few $300 drives fail within their first week of life, a couple the day after purchase.
As a result of this we always recommend that our customers purchase the drive which is least expensive based on the size they need. There does not seem to be an appreciable cost-benefit advantage for buying the more expensive models at this time. Of course, always backup your data regardless of the drive you buy, in the long run this will save you more money than any investment you initially make on a drive purchase.