I really not think you can find excuses for the person who take the swamp first. It's just not the optimal play, even by considering other survival card with the arguments said by others persons here.
(and the argument "choose one bad card (6), so you will not be targeting, so your teamates will be targeted" is not valid
7 is nearly always my first pick, gaining some card is really powerfull. And I really think at 5+ players, if you are the only one who used the rover power, you can said to the creature "I will go 7 this turn, enjoy.". The tempo loss by putting the creature token on 7 seem (for me) not worth it considering there is a good chance another player will be able to use the power of 5 or all players will have one free turn with a good effect.
9 seem good too, but just giving some will to players who are already in a bad spot will just not do much, they will still be on a bad position.
8 seem good on late game. Not cause it increase in value, but because others card decrease on value : 5 is just a little better than taking back another card, 7 give less time to use some card, 2/6/10 doesn't do much on the last 2/3 turns. Only the 9 have more value too since it give more space to try to have 1 will on the maximum of players at the end of the game.
I sometimes have a choice between 7 and 8 as first choice (or second) at late game, I already did some 8 pick.
Or even just with the face B, if the creature token is already on the nothing/artemis/nothing/artemis part perhaps 8 is better than 7.
For the swamp 6, I still don't know if a team should take only one 6 or two 6 since 6 is rarely discarded compared to all others card except 2.
7>9>6>10 & 8>6.