No treatment is better than the other, as both of them have their pros and cons. Depending on the characteristics of each couple and the origin of their fertility problems, IVF or ICSI would be more advisable.
For example, the most severe cases of asthenozoospermia should be treated with ICSI to guarantee a minimum number of chances for success. On the other hand, when the woman suffers from problems with ovulating or blocked fallopian tubes, conventional IVF can help solve the problem successfully.
Conventional IVF is more similar to natural conception and requires a higher degree of gamete manipulation. However, ICSI helps patients make a step forward toward pregnancy, as the egg-sperm binding is done manually.