My opinion: Solo both portals at the same time. Maybe send an extra in for a few seconds to fire off a few rockets then leave if the two soloers aren't 100% competent at soloing. This is easily the quickest most efficient method IMO.
These are the 3 main strategies ive seen used with only mild variations, so if you use a method similar to one of the above vote for that one.
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I usually go in alone while everyone else defends the portals. When I come out, I give the relic to someone else and I go for the next one. That makes everything 1000x easier. But that's just me.