Depends on the item, and what level you are. I used a level 13 Stormfront until I was about 27 or 28, but there's not a chance a level 40 version would hold up at 50. Class mods and relics can hold up a long time if you get an awesome one
EDIT: I'm an idiot. Misread the title as a more general question. My answer is still the Stormfront, though. Love that thing.