Olmo
Which has a chance of destroying the source with 1 sec to go losing you XP not to mention the possibility of wrecking whole area :)
I always kill the source node, always. I get slightly less mats per node on average (13-17 mats) but I can dig two nodes in about the same time someone who digs the timer can dig 1 node. That means in the time a homin digging on the timer can dig 15-20 mats (on a good node), I dig 26-34 mats. I spend less time digging for more mats and since XP is calculated on number of mats pulled, I also gain more XP over time.
As for depleting an area, I always have two areas next to each other to dig mats. Deplete the first one, dig the second and then return to the first which has restored by the time I've depleted the second area.
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Eldest, Order of the White Lotus