Pre-flight hassle will often make or sour my flight more than anything during the flight.
So, for example, if the person in front of me at SVO turns out to be checking in his entire football squad, I will spend the entire flight to AMS thinking about my letter of complaint (no matter how unfair). Or if there is a misunderstanding about the weight of my hand luggage at NCL, my mood will be sour all the way to HKG.
On the other hand, if check in was a dream and I have got a really good seat, I will calmly accept waiting for a slot with engines off in a remote part of NCL even though I have a pressing appointment at LHR. Or if there is a problem with my flight from MEL to MAN and QANTAS bend over backwards to get me to SYD for a suitable connection, then I will bless then for the entire flight.
During the flight, cheerful cabin crew is the most important thing. Not so fussed about chatty because I like my own company, but a smile and helpfulness really makes the flight.