This is a hot topic in our household as I am a certified Airplane Geek and probably know way too much than I should about this.
For short-haul in Europe we typically will use British Airways, but only redeeming with Avios. Easyjet at a push, but no to Ryanair (I hate Stansted). Norwegian is also usually a strong contender, although Gatwick is rather gross. Otherwise I am usually pretty open to trying new carriers across alliances.
Long-haul - it depends on route/time i have to spend/desire for higher class of service. You can get better fares with better service flying out of any major EU city for the most part, even doubling back into London on BA. SAS premium economy was a fantastic product that we took last year to Los Angeles and are considering again this year for trip home to Chicago area (actually going north of Milwaukee, but there is never a good fare into MKE). Sure its an extra leg into Stockholm (again, using Avios) but it works for us given family situation as we can see both sets of parents on one trip.
I just flew Virgin (economy) this week for the first time in 15 years after an awful experience and declining standards and found it quite decent with an excellent crew and service pattern, better inflight entertainment and cleaner aircraft than BA. Food wasn't much better, but their bar service sure was. But - they don't fly to where I need to go in the US.
Delta is the only US carrier I would consider, although partner had a good experience with AA more room in coach thing. United is a hard pass.
Going east - ABBA - anyone but BA. Trying Qatar in the fall to Singapore and partner just had a really good ride in economy on ANA to Japan.
For me, getting on a plane is part of the fun/experience and I want to try new things rather than just get to where I am going as fast as possible (with some exceptions). Its a bit difficult given Fortress Heathrow to avoid BA, but we sure try our darndest!