You should definitely choose JPM. JPM is in a better position at the laste league table for 2010 both DCM and ECM. Citi are facing troubles esp. with huge obligation to US government.
btw, I don't think any IB will have an easy job, you get what you deserved for and paid for what you contributed. As fresh graduate, why not stretch yourself for more experience!
I have a friend did intern in JPM HK last summer and got the full time offer too.