North Ave. is the locus of activity for the Air & Water Show.
I live just north of Belmont and see the beginning & end of a lot of the flight activity. In other words, I see jets heading to/from North Ave., see them getting into formation, turning around, etc., but have to crane my neck (or miss entirely) to see the more vertical stunts such as the sky divers, etc. I'm not sure how far south you can go for optimal viewing.
If you're at the Elysian (I don't know of anyone in Chicago who calls it the Waldorf Astoria, unless they've just started to rebrand it), I suspect your east/northeast view would be obstructed by the buildings along Michigan Ave. However, there might also be some obstructions looking to the north, too.
The Sutton Place Hotel and Ambassador East are further north--putting you closer to the action--but to the best of my recollection neither has balconies and each may have visual obstructions.
Your best best--assuming you can guarantee an east view on a high floor--would be the newly reopened
Hotel Lincoln on Clark St. just north of North Ave. There's nothing but park & trees between the hotel and the lake. No balconies, however. They do claim to have rooftop yoga classes, so you might also find the rooftop is open during the air & water show. Do realize, however, that a rooftop deck is no guarantee of a fantastic view. My building has a rooftop deck, but the eastern portion is off-limits for various reasons.