Agile or Waterfall? Which development methodology should I use in project management ??

I would extend Alan's answer.
In reality most waterfall projects that are large become unwieldy.
They are late, the requirements change, and no one ever really does all the changes correctly.
In other words, we don't tend to do waterfall well.
Therefore Agile is usually much more cost effective even for large projects.
Provided, always provided the control points needed for Agile are applied.

This depends on how big the project is and the effort needed.
If the project is too big that you'll be stuck in just perfecting the requirement and creating tones of specification, i'll suggest waterfall.
However, if you have a tight deadline and lesser documentation, better use Agile.
Less talk, less documentation, more action, more development.
I've used both methodology in my projects.
In general, I like using Agile as its faster in terms of development and output.

I have used both and i found Agile to fit in most of the occasions properly which lead me to handle the work and manage the team effectively.
Idea behind agile is to divide the work in small chunks easy to manage followed by number of sprints.
It provides the perfect grip and don;t let it loose over the span of time.
I should recommend you to go for Agile.

I prefer Agile.

Defintly Agile as it supports all c's of automation and thats needed in new software industry.

- Continous Planning

- Continous Development 

- Continous Testing

- Continous integration

- Continous Deployment

Issue with watefall model is timeline of delivery.Its hard to manage.