This is really a question that has to do with pace of play. Scoring and handicapping can handle inequities in difficulty, but only PACE and FLOW variables can manage the time it takes to play. This is important if the 18-holes are to be used interchangeably where players are set out on opposing nines with an expectation to meet magically at roughly the same time to swap nines. So, it really does not matter provided the set-up of different nines with different PACE RATINGS can be adjusted.
If I were to answer directly — from a play perspective — I would vote for a more difficult front nine as this is generally when the player has more energy and zest. Plus, there may be less risk taking on the outbound holes, whereas coming back home — with more shots under one's belt — there is apt to be a bit more "go for it" mentality. "Easier" tends to go hand in hand with gambling. More difficulty tends to bring out caution and restraint.