Software development, like any other business process, has certain targeted goals which must be achieved in a fixed time frame. There are various strategies for achieving these software development goals. Two of the most popular software development models are 'Waterfall' and 'Agile'.
Waterfall Vs. Agile Model Comparison
Waterfall Model
Waterfall Model
Waterfall model in software engineering, got formally introduced as an idea, through a paper published by Winston Royce in 1970. However, it's ironic that he himself had introduced it as an example of a flawed software development method, that's vulnerable due to its many shortcomings. Nevertheless, every methodology has takers and this model has been successfully implemented by many software companies. Waterfall model philosophy was inherited from the hardware manufacture strategies and construction strategies that were in practice during the 1970s. That's why, it has a very structured approach to software development.
Agile Model
Agile Model
The agile model of software development, evolved in the 1990s, when developers decided to break away from traditional structured, segmented, bureaucratic approaches to software development and moved towards more flexible development styles. The 'Agile' or 'Lightweight' methods as they were called, were formally defined in a research paper by Edmonds in 1974. Some of the most prominent and popular agile methods of software development, that subsequently evolved, are 'Scrum' in 1995, 'Crystal Clear', 'Extreme Programming' in 1996, 'Adaptive Software Development', 'Dynamic Systems Development Method' in 1995 and 'Feature Driven Development'. In 2001, a group of pioneers in agile software development came together and declared the 'Agile Manifesto', which is a set of canonical rules of sorts, for agile software development methods.
Conceptual Difference Between Waterfall and Agile Model Comparison
Waterfall model, as the name itself signifies, is a sequential process of software development. Just like in a waterfall, the water progressively falls from one altitude to the lower, in a similar way, the production cycle progresses sequentially, from one stage to the other.

The phases of software development, in this model, are as follows: requirement specification, conception, analysis, design, coding, testing & debugging, installation and finally, maintenance. In this sequentially structured approach, the development team goes ahead to the next stage of development, only after the previous stage is fully accomplished. Software development companies, adopting this model, spend a considerable amount of time in each stage of development, till all doubts are cleared and all requirements are met. The belief that drives this kind of software development model is that considerable time spent in initial design effort corrects bugs in advance. Once the design stage is over, it's implemented exactly in the coding stage, with no changes later. Often the analysis, design and coding teams are separated and work on small parts in the whole developmental process. Emphasis is placed on documentation of every software development stage.

Now let's look at the agile software development method. Compared to the 'set-in-stone' approach of waterfall development models, the agile breed of models, focus on 'agility' and 'adaptability' in development. Instead of one time-consuming and rigid development schedule, agile models involve multiple iterative development schedule that seek to improve the output with every iteration. Each iteration goes through all the steps of design, coding and testing. The design is not set in stone and is kept open to last minute changes due to iterative implementation. The team structure is cross functional, closely knit and self-organizing. The design idea is never totally frozen or set in stone, but it's allowed to evolve as new ideas come in with each release. Less importance is given to documentation and more to speed of delivering a working program. Customers may be provided demonstrations at the end of each iteration and their feedback may determine the next course of changes in the next iteration. The iterative cycle continues till the customer is delivered with a product which exactly meets his expectations.
Difference in the Efficiency of the Waterfall and Agile Model Comparison
In the ongoing comparison, let's see how these two ideologies compare with respect to development efficiency. Efficiency is decided by the quality of ultimate software product, the number of bugs and the development time consumed. Through my own research into the working of both these models, I found the agile models to be more efficient than the waterfall model, due to their adaptability to the real world. The 'One Phase' and 'Rigid' development cycle, makes it difficult to make last minute changes in requirements or design. While the agile methods, due to their iterative and adaptable nature, can incorporate changes and release a product, in lesser time. Of course, agile models are not perfect either, but they are certainly more widely applicable than the waterfall model. Of course, the expertise, skill set, attitude and ability of team members working in the project is a prime factor which affects efficiency. Be it agile or the waterfall model, that's adopted, communication within the team members and with the customer, goal setting and better planning contributes to improving efficiency.
Suitability of the Waterfall and Agile Model Comparison
The waterfall model is suited for development of programs that are already stable. That is, their design doesn't need a major makeover. In situations where the designers of a software program can accurately predict the flaws that may arise, in advance, waterfall model is the appropriate choice. Despite all its flaws, its design is easier to manage and the development costs can be ascertained beforehand. It is a natural choice when the customer has provided a clear list of requirements, which are not likely to be modified. On the other hand, when the customer is not clear about his requirements or expectations from the end product, adopting Agile model makes sense. The experience of the team members in handling the specific type of project should also be taken into consideration. If the developers are experienced enough at handling that project, then Agile approach is a better option.

Another point of consideration is the time frame within which the project is expected to be finished. When the time frame is long enough, choosing the Waterfall route is possible, while rapid delivery projects are best handled in the Agile way. Cost of the project is another point of consideration, which may influence your choice.

Agile models are applicable in every area of software development. It depends a lot more on the team effort of above average programmers, than relying on a few expert programmers. It's best suited for web based applications where its iterative nature helps in incorporating and correcting the various bugs that arise over time. Choose a model that best suits the experience of your team.