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 recently joined a new team who always do one at a time. So while 5 of them were pratting around doing mars, i got bored and opened up venus. Took out the gatekeeper with my ice breaker (dont have a gally) and ran out the gate with the relic before the praetorian managed to close the gate. Unfortunately i died to the praetorian since the cleanse doesnt charge fast enough, but i just self-revived. Everyone was like 'right people places now we need to do venus' and im just sat in the middle with the relic and they didnt even realise. Fml.