The players with the worst strategies (i.e. using a buff in the last round, not targeting the nearly dead enemy with the magic missile, etc) are usually the adults who have been playing 10 years or more. Same thing with the complainers.
The teenagers seem to take it in stride - not expert players, but they largely remember their abilities. If they have an issue, they act recklessly to pull off plans - which at least keeps it interesting.
I have 6 players. That's only one more than is recommended for 4e - and that sixth player often misses half the session because of her work schedule.
All the players are interconnected - so I can't uninvite any of them (siblings, spouses, etc.)