If you are truly new to both parks, just know you will never see it all in Orlando in seven days. So, you have to prioritize and make choices. If you choose to do all WDW and really immerse yourself, you still will NOT see all of WDW. But, you will get a pretty good feel on if you want to return or not, and that is important. That being said, my opinion alone is that you will know that doing 4-5 days at WDW as well.
So, throwing in a day or two at Universal to get a taste of it might be a good option as well. You know, a nice sample platter of parks to know how to plan the next Orlando vacation.
As for my family - we are 1) Universal, 2) Discovery Cove with Sea World/Aquatica (my kids favorite one day park in Orlando is Aquatica), then 3) WDW. For us - if WDW didn't have the princesses, we would probably never go. Even at the very high price, we still pay to do breakfast in the castle at least once every 2 years. I'm a sucker for a dad - it makes DD happy, so we budget it in.