I want to find out which hard drive in my computer is fastest, so I can put my OS on it. I have tried several utilities that do this in the past. What's a utility that makes this task relatively easy?
Check out HD Tune:
I think the free version will only tell you read speed though.
There is also DiskBench which is free and it will let you measure read and write speed in a realistic situation, among other things:
The ATTO Disk Benchmark performance measurement tool is compatible with Microsoft Windows. Measure your storage systems performance with various transfer sizes and test lengths for reads and writes. Several options are available to customize your performance measurement including queue depth, overlapped I/O and even a comparison mode with the option to run continuously. Use ATTO Disk Benchmark to test any manufacturers RAID controllers, storage controllers, host adapters, hard drives and SSD drives and notice that ATTO products will consistently provide the highest level of performance to your storage.
ATTO Disk Benchmark is freeware and portable.