dead rising 2 or off the record?

Off the record, has slighly more content

I think this as well as this should answer your question.

rather get your self "Dead Island" :)

Dead Rising 2 is better than Dead Rising 2: Off The Record, and it's expansion, Dead Rising 2: Case Zero is great.
But there isn't much difference between the 2, that's the reason why Off The Record got average reviews

I heard OTR is better because it has a sandbox mode

I think you should buy the complete pack if its goes to sale on steam :)

But for now I only played the normal one its really good :)

Off the record for sandbox mode alone I would say. Don't forget to use the coupon on the main page, brings it to 6 dollars.

nothing, save your money for better sales.