I forgot to mention - cranks are usually long term investments as far as bike parts go. You can move them from bike to bike (usually) and they don't wear out. Okay, the chainrings wear out, but usually not the crank. I used the same cranks for 5-7 years at a time, changing them not because they were worn but because I wanted something new.
This does NOT apply to anything that is not cold forged aluminum. And I have no idea how carbon cranks hold up.
So for aluminum it means DA, Chorus, and Record.
cdr