Are you using your heals for PVE or PVP? Dungeons or open environment?
For PVE purposes- VoB is fantastic... especially in dungeons. You'll add heals and damage when your group is stacked on a boss. Your party (especially in a trial) will rely on you for your VoB or other players who have Nova. If you're soloing in PvE- I'd recommend Soul Tether. You'll be able to disable nearby enemies and heal yourself while fighting them.
For PVP purposes- I use Soul Tether. (Not Soul Siphon) While Soul Siphon has an insta-heal to surrounding players, Soul Tether offers crowd control and a synergy that other players can use. If you use Soul Siphon, you'll offer a quick heal to your comrades and then get instantly jumped by the enemy. A dead healer offers no heals. ;o)
I hope this helps!
Want to enjoy the game more? Try both PvP (crybabies) and PvE (carebears). You'll get a better perspective on everyone's opinion.