5 exploding dice are worth 6 non-exploding dice. You can summarize this rule as:
If your edge is 4 or less, do the "add edge number of dice" option only when the missed dice are equal to or less than your edge.
If you have Edge 5, do the "add edge number of dice" option when there are 5 or less mixed dice. When there are exactly 6 missed dice, you should take the "add edge number of dice" if you really need more than 2 hits, and the "reroll misses" option if you more just want 1 or 2 more successes to hit a threshold [this is because the edge dice are spikier; you're more likely to get 0 hits, but also more likely to get 4]. When there are more than 6 missed dice, reroll the misses.
If you have Edge 6-8, do the "add edge number of dice" only when the missed dice are equal to or less than (your edge + 1).
There are some funny edge cases where you should do the 'add edge number of dice' option anyways - generally when you really need to hit an improbably high threshold. Like if you have Edge 1, 2 misses, and you need 3 more hits, you should go for the "edge number of dice" option since it's hopeless otherwise (but really, you should have predeclared edge!).