What’s the best way to get discounted tickets to Universal/Disney for a family of 4 for one day?
I've never been able to find any tickets less than what the parks themselves sell them for.
Do you have AAA? You could try them, though our local AAA is always the same as the parks. Even undercover tourist didn't have any tickets less than Universal itself (at least when we went they didn't).
No discounts on one day tickets.
Unfortunately Disney nor Universal will not discount their single day tickets, purchase them online or at the gates when you visit.
Currently 1 day 1 park at Universal Orlando is Peak Season - $132.06 (adult) and $126.74 (child 3-9), if you did both Universal parks in 1 day the cost is $190.64 (adult) and $185.31 (child 3-9).
June 1-24 is considered Regular Season for Disney so 1 day at the Magic Kingdom is $126.74 (adult) and $120.35 (child 3-9), 1 day at Epcot, Hollywood Studios or Animal Kingdom would be $121.41 (adult) and $115.02 (child 3-9).
Hope this helps!
AAA maybe. But outside of potentially invalid tickets, or attending a timeshare sell you have little chance