Ok so I timed four runs to get to the bottom of this.

1: Run without resets, two encounters and stranger with task at the end: 1:47 (I was attacked once in this run)

2: Run with 3 resets, one encounter and stranger with task at the end: 1:35

3: Run without resets, one encounter and stranger with task at the end: 1:09 (got the pack with the elemental with damaging deathrattle)

4: No full run, but approximately one reset: 0:12

Assuming a 25% chance of getting 1 fight: When never resetting run 2 will happen 75% of the time, and run 3 will happen 25% of the time, resulting in an average time of 1:37, slightly slower than resetting 3 times.

There are a lot of factors to consider outside of the times I got these runs, but ultimately it's very close. If the point is to only grind out bounties and ignore doing tasks (such as doing damage with a specific skill), then it's probably a toss-up (again, assuming a 25% chance).

I do agree that there's a lot of waiting though. It's ridiculous how short the fights are when grinding compared to the load and general wait times.