(btw, there's apparently enchants/set bonuses that decrease the potion cooldown)
(Argonian Passive) Quick to Mend: +6% healing received (Siphoning Passive) Soul Siphoner: +15% healing received from Siphoning abilities (Siphoning Passive) Soul Swallow: +10% healing received while skill is slotted
I tried both Siphoning and Assassination during the beta, and they definitely both have their advantages and disadvantages.
While I did generally manage to live longer as a Siphoner, I also had difficulty doing enough damage to kill my opponent. Maybe it was just my build-- I am not typically an avid PVPer, so this game will be a bit of a first for me.
In terms of doing heavy damage quickly, Assassination came out ahead. I didn't spend very much time PVPing with this build, but in PVE at least I was able to end fights quickly with very little health lost on my part. I think I may try Assassination again when ESO is released...