I've been using muriatic acid with a 31.45% concentration (from Leslies) lately since it is the most economical. Previously I used a type with 14.5% concentration, from my local hardware store and Home Depot, which was more costly when taking the strength into account.
I find that the stronger version produces much more fumes. I pour it in a glass measuring cup and walk around the pool slowly dribbling it out as I walk. I try to avoid being downwind of the cup. I will take a deep breath and hold it for a while as I walk. When I need to take another breath, I stop and carefully take a small sniff to make sure I don't have a cloud of fumes near my face, before I take another deep breath. This works for me, and I don't have a problem doing this.
I pour from the bottle into my measuring cup (while holding my breath), while I am near the pool, and then dip the bottom of the bottle in the pool before setting it back on the patio. Then I walk around the pool, dribbling it so there is not much in any one place. I was nervous about pouring all of it in one place in front of the return jet. I also avoid pouring acid over any of the shallow places such as swim steps and sitting ledges, since it is heavier than water and it sinks.
I think that when I was using the weaker muriatic acid previously, it had much less tendency to produce fumes, and I rarely detected it when I breathed through my nose. I don't know if that is my imagination, but if true, it might mean that the weaker version is more convenient and safer to use, even though it is less cost effective.