Just as with the WDW parks, you can have a wonderful day at SeaWorld, but you're not going to be able to do everything. You have to decide what your priorities are.
Decide which show you most want to see, if seeing a show is your priority, and then plan the rest of your day around that. If you want to ride one of the major attractions, either do that first OR do it during the day time Shamu show (which is the most heavily attended). Decide which animal exhibits you most want to see, and if feeding animals is a priority, check what time(s) feeding is an option.
We've been twice during December and the crowds are NOT bad, but the way the timing of the shows and animal feeding opportunities are set you just cannot do it all.
SeaWorld is a gem of a park, and you'll get the most out of it by setting your priorities ahead of time. Enjoy!