Soul Tether or Siphon on a self-support Stam NB?

[Jewel]

I'm making a Nightblade with high fixation on self-heal using abilities that steal health and gives it to me and a little side focus of healing others, letting my healing abilities make up for lost health.
As it stands, I use Swallow Soul, Bloodthirst, Blood Craze, and Killer's Blade all to heal myself and Healthy Offering to heal my group. Should I go with the more selfish and slow Tether while also dealing more damage against large groups, or go a bit more support and give myself and teammates a huge amount of condensed healing with additional healing received buffs?

[737]

Soul Tether if you're dps.
Soul Siphon if you're tank or healer.