What an ARM actually is
An adjustable rate mortgage is fixed for an initial period, commonly five, seven, or ten years, then adjusts on a schedule tied to an index plus a margin.
Caps limit how much it can move at the first adjustment, at each adjustment after, and over the life of the loan. Read those caps as the worst case you are agreeing to, because occasionally the worst case happens.
The honest test
Ask one question: if the rate adjusted to its ceiling, could I still make the payment comfortably? If the answer is no, the savings today are not worth the exposure later.
For most buyers who expect to stay past the fixed period, a fixed rate is the calmer choice. Certainty has value even when it costs a little.