I find it hard sometimes to remember what Generations even came with. Once I take out the Imaginary Friends, the royal court, scolding, boarding school, midlife crises and memory scrapbook system from my game, it turns into a very unmemorable pack for me.
Looking at the wiki it brought in new woohoo spots, after school activities, field trips, new parties, the daycare profession, the costume chest, online dating and a couple traits and LTWs. I'm sure if I ever played without it I might miss school activities and field trips but apart from that... it feels very empty.
I agree on what others have said about using Nraas Retuner to stop the autonomous royal court interaction.
The three you listed are all equally great EPs. I would buy them all but if you're doing it one at a time I would say Ambitions first.