I love IL and SE, truly. I use them all the time and if I had to reinstall 4 one pack at a time they would be some of the first. However, if we are talking strictly gameplay then EL has more. I know it gets a bad rap with all the bugs it launched with, plus some people just do not like NAPs (there are a few I never use as well), but it has much more content for the other worlds than SE or IL.
SE and IL are very much destination worlds. You will have to live in or break your back visiting these worlds to get your money's worth with the packs. The skills are not completely exclusive, but if you want to swim, climb, or snowboard, only a few worlds have it.
EL, in comparison, offers its eco gameplay to all worlds. Each has an eco state now, each neighborhood can have different NAPs defining the neighborhood, and there is eco gameplay to back these up (a huge selection of upgrades, new furniture replacements like an automatic watering planter, water and power collection/production for bills, community lots). I find EL essential to do any sort of off the grid play. That is part of why I find it to be such a great pair to IL, that and conservation.
So while I love SE and IL, I cannot recommend them over EL.