The issue you have is that there is no hotel that really fits the bill as being close to Universal and Disney as they are both basically the opposite sides of the 'LA area'. I would consider staying in more than 1 hotel if you want to be close. Getting across LA can take hours in peek times the traffic is insane.
I would just have a look at Expedia and go from there, chain hotels will be pretty consistent across the board. A few things you just need to watch out for is that:
Parking is often for free
Included breakfast can sometimes be not great, really depends on the hotel
Traffic is stupid, check out some of your proposed routes on google maps at the times you expect to travel
LA its self can be proper rough as the above poster indicated, tends to get better generally the further away you get.
The three nights I stayed in LA were well outside of LA itself:
Hotel Indigo, Anahiem. Reasonable price, great for Disney and free parking. Cheesecake Factory down the road for cheap eats.
Courtyard by Marriott Santa Maria, nice big rooms, paid parking, had breakfast included and it was fantastic but expensive if you have to pay. Hotel is not too far from Disney but gives good access to San Diego attractions such as Lego Land and Sea World about an hour away.
Homewood Suits by Hilton, was good but this was way out of town in Oxnard but I am sure they would have other locations better for you. Big clean rooms, could self cater if from here if you wanted to.
