All three medications belong to the same class (phosphodiesterase type 5 or PDE5 inhibitors) and work similarly by increasing blood flow to the penis, facilitating an erection.
All are effective for treating erectile dysfunction (ED). tadalafil 20mg is one of the best solution
Key Differences:

Onset and Duration:

Viagra: Starts working within 30 to 60 minutes, lasting for 4 to 6 hours. This makes it ideal for situations where you want a predictable window of effectiveness for sexual activity.
Cialis: Takes effect within 30 minutes to 2 hours and can last up to 36 hours in some individuals. This offers greater spontaneity and flexibility.
Levitra: Similar to Viagra, Levitra starts working within 30 to 60 minutes and lasts for 4 to 6 hours.