If you only want to use Sunforge Lancer than which general you use depends on you want to games to play out.
Argeon is more aggressive and will tend to use Sunforge Lancer’s buffs to pressure the opponent while using his BBS to allow Healing Mystics and Azure Heralds to trade effectively. His BBS is used to buff minion so that they trade up in the early game and apply more pressure in the late game.
Zir’an doesn’t trade minions on a 1 for 1 basis often. Rather she uses her high health minions to value trade and then heals them up to produce card advantage through combat. Zir’an will be more controlling by using Sunforge Lancer’s buffs to make trades that her minions couldn’t live through and then healing off chip damage from her minions.
As long as Sunforge Lancer is your only healing synergy card it won’t really matter what general you use. Between Sundrop Elixir, Healing Mystic, Azure Herald, Martyrdom, Scintilla, Holy Immolation, Trinity Oath, and CIrcle of Life you more than enough healing procs regardless of which BBS you prefer.
If however you want to play Lightchaser, Lucent Beam, Sun Riser, Sun Sister Sterope, Gold Vitriol, or Excelcius than you should use always use Zir’an as her BBS triggers those effects more reliably and more importantly makes it easier to double proc the effects.
Here is a casual Healyonar list I ran back when Rise of the Bloodborne first came out. It’s not tuned, competitive, or made for the current meta but it is something to look at if you need it.
Summary
http://i.imgur.com/eNMHLjm.png