Like operating systems, everyone has their own 'relgious' bent on which one is the 'best'. Digikey and Mouser have the widest complementing selections, whereas Newark and Allied focus on site layout, supplier relations and service.
The worst place a maker can go after getting a paycheck.
Every battery for everything ever.
I always found it somewhat hard to find the right inductor cores. If you want to do your own magnetics (voltage conversion, chokes, etc), this is a good place to start.
Another good magentics resource