As far as discount or benefit goes the first one is the best one. if you buy a Forum Leather Modular sofa for $2999 you get a $1000 voucher to spend instore. It works out to be a reasonable offer providing you were planning to spend the other money on stuff anyway.
The other offers...
Buy $500 in the homewares section and get a $50 voucher. Bit piddly if you ask me. Spend $1500 or more on the Cancun Range and get a $300 voucher to spend instore. Buy the Lucas Leather Modular sofa for $2999 and get $500 to spend instore.