You'd have to specify 'unpleasant'. Seats or service?

AA has the best legroom.
BA has one of the most cramped. But okay service and food depending on route.
IB (ditto above)
CX also has cramped seating but good service, food and inflight entertainment
QF - well you know QF.
AY - has good legroom too. Service so so.
LA - no experience with them. But I heard good service and food.