When done correctly, at the high end, there really is not a difference. However hard styles tend to enjoy crushing and smashing uke more, and soft styles tend to enjoy running uke to death.
As I continue to progress in Aikido, the softer that I become, the harder that I can (if I so choose-and I ofter do if appropriate--no apologies) throw. To me it is much more about having the proper attitude to deal with an attack and over time adjusting one's technique so as to not become "stuck" in kata responses or attacks and to make sure that there is indeed AIKI in your technique.
That way it will be more fluid, dynamic, and responsive to whatever life throws at you whether it be on the street or in a relationship. Just because one ignores one application or another of AIkido doesn't mean that it won't be thrust in your face at some point.