If you are going to limit your choices to those two, I'd go with the 989. The Triton has a 90W limit on charge output, so unless I'm mistaken, charging the 3S 8Ah pack at 1C (8A) will really be pushing the limits of the charger. The triton also tops out at 5S. The 989 should be able to do a max of 10A, probably up to 5S at that current, so 3S at 8A shouldn't be a problem.

Be sure to get a balancer too. I'd recommend the Hyperion LBA10, if you are going with the 989 or a Hyperion charger (which wouldn't be a bad idea to look at).