If you can do the concentric part, then yes, that would be better. But in some exercises, especially without a spotter, you just won't be able to do it. In that case, just the eccentric part is enough. This is because the eccentric part is the part of the lift that "creates" more hypertrophy. However, you really should do metabollic work after. Metabollic work is simply doing low-weight/high-rep sets. Among other things, this triggers far better nutrient transport to the muscles.