Short answer: I am currently doing option 2.
Long answer:
I would say it depends on your mental condition(s). There are some conditions, specially transient ones where you could get some "as you go" counseling, apply the recommendations and review if needed. Others like depression, ADHD, GAD, etc I would recommend (based on experience as ADHD+GAD patient) to stick to a long-term commitment.
Taking myself as an example, currently I have a "subscription model" with my counselor/therapist where I pay in advance for a specific number of sessions and get 20% discount from normal session price. It is important for me to really identify the deeper issues as well organize the inner complications of living with ADHD + GAD, also important for accountability as in my case the therapist gives some "tasks" to me in a weekly basis.