To me, I think both are just as bad. But the results of our actions, or more accurately put, the karma that comes back to us depends on our intent. Both methods of insinuating and accusing can bring harm to others, depending on our motive, intent, actions and feeling whilst carrying it out and after.
Insinuating, I feel is more like purposely stirring up and creating problems/rumours to throw others out of balance or to start a new rumour. Basically, its to play with other's minds regardless of whether evidence is at hand or not.
Accusing is to blame others without any evidence at hand.
Dictionary.com's definitions:
Insinuate:
1. to suggest or hint slyly
2. to instill or infuse subtly or artfully, as into the mind
3. to bring or introduce into a position or relation by indirect or artful methods
Accuse:
1. to charge with the fault, offense, or crime
2. to find fault with; blame.
Both are equally bad, but I feel insinuating is worst as it is playing with other's minds.