Well, thing is, Liana's NOT f2p here...
And yes, you totally should use your Alissa first, unless you mincosted Iris, or are deploying healers in the late-game, in healing-intensive environment where silvers don't cut it anymore (rare), or when cost is non-issue.) Min-cost Alissa is baeMin-cost AW Iris doubly so
There will be a couple of event plat healers and even more healer-hybrids (unless we skip them like Noel&Kagura)