The "best" insulin is the one that is best for you. And the gold star insulin is the one that we sed to produce before we got Type 1 diabetes,
We are all different and the only way of finding out what suits you best is trial and learning.
However, it is odd that a fast acting insulin which lasts 4 hours can make you spike when it runs out. Have you done a basal test recently to ensure that your basal dose is high enough? You may be covering it with the Fiasp for 4 hours. Bear in mind that your basal needs may differ during the day and night.
The other thing that surprises me as a long term Fiasp user, is that you need to take it 25 minutes before eating. I only need to prebolus that early if my BG is in double figures. If my BG is "in range" I can bolus when I start eating to avoid spikes and if my BG is in the 4s or 5s, I have to bolus after eating.
However, when my BG is in double figures, it can feel as if I am injecting water and then suddenly it starts working.
I really like Fiasp but when I switched from taking NovoRapid for more than a decade, Fiasp took some getting used to because if this variable activation speed.