I'd slightly rather pair the 8. Really, the two situations are almost identical. If you pair the 8, you have a 7 kicker, and there are 6 better kickers. If you pair the 7, you have an 8 kicker, and there are 6 better kickers. The only difference is if you're up against 77. With a pair of 8's and a 7 kicker, you beat 77. With a pair of 7's and an 8 kicker, you lose to 77.