for examples with N taskinstances look at the testcases. Especially the WF14 and 15 testcases.
The difference/similarity depends on what you want to achieve. the one tasknode has the advantage that it can cancel other tasks if e.g. one is completed. So you can do a 2 out of 3 (assign the same task to multiple people and if e.g. 2 of 3 have completed the task the processs continues)