We also live on Oahu and I would also suggest Germaine's over Paradise Cove. We went to Paradise once and ever since went back to Germaine's (I have also been to the one at Hale Koa). Like Hanna said, they do not skimp on the liquor and lots of times if you talk to the bartenders they don't even take the drink coupon (or I have given them 1 when I should have given 2). You will get 3 coupons for drinks per person if over 21....My suggestion also is go to the gift shop and buy the Germaine's souvenir glass for $6.00, it is about 2.5 times the size of the plastic cups they use for the drinks and they will use that instead.
I don't know your itenarary, but are you going to be in port all night? That would be the only way to go to a luau.