I'd use (2) Jager 250w heaters. If you use GFIs (which you should), set up 2 GFIs if possible and place each heater on a separate GFI.
This way:
1. If one GFI blows or one heater fails, you don't loose heat.
2. If one heater sticks on, it won't "cook" your tank as fast, giving you more time to intervene.
I've never seen a Jager fail in either "on" or "off." I've seen Wons fail, that's why I made the switch.