I've always been bored with SeaWorld, personally. Of course, I'm a native local and I've seen those animals roughly a thousand times, so take that for whatever it's worth. I'm not necessarily a "thrill-seeker." In fact, I don't even ride looping coasters (check Kraken off the list.) But as your average 20-year-old theme park enthusiast, I need actual rides to sustain my interest. Frankly, I'm not exactly bowled over by SeaWorld's selection.
I can't disagree with you. As a 26-year old guy, Sea World bores me. But...
Journey to Atlantis was an admirable attempt at a legitimate marquee attraction, but compared to it's competitors, it's pretty substandard. Especially considering how much worse it's gotten since opening year. But that's Busch's maintenance standards for ya. I won't even go into the disaster known as Busch Gardens.
I can't disagree with you there either. I HATED Journey to Atlantis. But, I thought I was the only one...go figure. But...
My suggestion would obviously be Universal, mostly for the sake of the older kids (I'm age biased, you know.) Contrary to the (often misinformed) opinions you'll get on this board, there are still things perfectly appropriate for the little ones to do at Universal. Actual rides, among other things. All they'd be doing at SeaWorld is watching the animals. SeaWorld has three full-size rides, all of which are thrill rides. The young ones can't ride them and the older ones will be done in an hour, tops. There are kiddie rides, but they are all of the barely themed traveling carnival variety. Quite Six Flags-ish.
I still think that kids, for some reason, are enthralled by animals. Maybe it's just me, but I remember my brothers loving this park (same with my little cousins a few years ago), while I sat there bored out of my mind. I guess what this comes down to is, who are you trying to make happier. The older kids or the younger ones. If it is the younger ones, I think Sea World is a better choice -- if they like animals. If it's the older ones, Universal without a doubt.
Gee, I sure hope they don't like any of Universal's kiddie properties (which there are more of than many would like to believe.) They won't be able to enjoy any of them by that point.
No one's going to change my mind that Universal has enough geared towards kids. I'm not a parent yet, so maybe I don't know what I'm talking about, but two play areas and a kiddie coaster (and some other things that I'll list below)do not equal what Disney has to offer. Like I said before, ET is one of my favorite rides in any theme park, but the Woody Woodpecker roller coaster is not going to draw me in. I despise Shrek (and will hopefully pass that hatred on to my kids

). Hanna Barbera's simulator was infinitely better than the Jimmy Neutron one they have now. Suessland can be enjoyed by all, not just by the very young. I guess my point is that, as is evidenced by your post as well, as youth get older, they tend to be bored more easily with Sea World. As they get older, there is more to enjoy at Universal and less to enjoy about Sea World. A 9-year old can still enjoy ET or (god-forbid) Shrek or the Cat in the Hat ride just as much as a 4 year old, but that 9 year old can also appreciate Men in Black and Jaws and Ripsaw Falls more, too. I mean, why not see Sea World when young kids can enjoy it.
I realize it's a matter of taste and I'm not stating these things to try to sway your opinion, but it's simply my opinion. A 2 and a 4 year old are going to miss out on some of the best attractions Universal has to offer. Like I said before, I'd just stay at Disney...but if I had to choose another park to go to with 2 kids below 5, I'd pick Sea World.
But, back to the OP, I still think it matters who you're trying to make happy by leaving Disney -- the older ones or the younger ones. Sure, there are things that the young ones will find to do at Universal, but I still think there will be more for them to enjoy at Sea World.