Reliability of external USB hard drives?

From the responses here I assume the higher the hard drive storage the more likely you may have a problem and I guess the higher the speed may also to contribute to heat buildup and wear on the bearrings etc.

My question is..I am buying a new computer and and I do not expect to store stuff on the HD other than the operating system and neccessary programs like Photoshop and then the stuff will be put on Blueray.

What size and speed is considered most reliable currently...Thank you for reading this...Jeff