Swalla

I use Ifly Schedules's Career mode, helps give purpose to the flights and adds in some extra challenge with the landing limits, exhaustion and ascent/descent limits. It also helps go to new regions of the world and visit a lot more smaller airports especially. And the biggest pro for me is how much the developer listens to feedback and suggestions and how willing he is to implement almost any requested feature. It is currently in alpha but looks really promising and fun. I usually alternate career and free flight days so it ensures I never get bored of either and being able to do both on the same website is a really helpeful thing.