Back Pack Or Side Pack - Come And Look At The Vanguard Bags
So far the best plan for this has been to buy a Citroen H van and hire minions to load it and unload it for you. Minions are a good investment.
If your tastes are for a little less to pack - say you are going out for landscapes or political riots - we recommend a carrying bag. If it's your shoulders and back rather than those of the minions, get a good one - one that spreads the load enough to make it comfortable.
Vanguard make a wide range and two of their bags - the Vojo 22 and the 2GO 39 are particularly suited to the mirror-less systems. The former is messenger-style, dependent upon one shoulder while the latter is a single strap backpack. They are available in green or black and feature any number of ingenious compartments inside to swallow the accessories. ( Which you will find in three years...)
The reason I selected these today was as a result of having lifted the very fashionable bag of another manufacturer and reflected on how much unsprung weight it was - a task in itself to haul on your shoulder even without any camera or lenses inside. The Vanguard bags are lighter than this but have a tough enough internal structure and padding to protect the gear.
I can't say which carry configuration is better for you - you'll know how your skeletal structure copes with stress at different points. Of course if you are looking at an equation that places an enormous amount of gear into a bag and makes you trail it for hours, you might well consider the roller cases - or hiring minions.