Here, let's elucidate the various ways you can apply to college including their relative pros and cons. Generally, the differences between the different application types spring from when you can apply. The best rule of thumb, however, is to apply as early as possible, given that you are well prepared. The universities leave the choice up to you as to which type of decision you want to use.

Early Action (EA)
You apply in the middle of November, and usually hear from the university in mid-December. Sometimes, however, colleges will say that they would prefer having the application earlier (Harvard requests sometime in October). Admissions-wise, there should be no difference as long as you apply by the absolute deadline in November. Three possible things can happen: acceptance, rejection, and deferral. Deferral means that your application will be considered with the rest of the "Regular" applicants. A substantial proportion of Early Action applications are deferred, though a few are accepted and rejected each year.

A special type of Early Action is called Single Choice Early Action (SCEA), which is used by a few schools, including Harvard. This option means that you can only apply to one school via Early Action and therefore severely limits your options.

Pros: If you get in, joy! You're assured a place at least one school that you like and you have the option of applying regular decision or just relaxing for the rest of senior year. Note that your grades and achievements cannot be significantly adversely impacted or else there is still the possibility of having your admissions letter rescinded.

Cons: You have to be ready to apply early on in the college application process, which means that you will have to have all the essays, recommendations, and sundry other items good to go. Also, some of your achievements in later senior year will not be available. Still, deferral results in the same process as regular decision. And rejection will at least lessen your waiting period and give you the chance to apply to other schools that you have a better chance at.

Early Decision (ED)
This is admissions option is similar to Early Action, except you can only apply to one school early and if you do get in, you are legally bound to go there (and this is a serious legal obligation). If you are accepted, you also must withdraw your application from all of the other colleges you applied to. Otherwise, the college will rescind its admissions offer.

Pros: To universities, applying via Early Decision means a lot, as it shows you are committed to attending that university. You will have a better chance of getting in than otherwise. Also, look at the Pros section for Early Action.

Cons: You can apply to only one Early Decision school. JUST ONE. Thus, you must make sure that school is the one you are committed to going to. Now, you might be tempted to apply to two or more ED schools because you think that there is no way that they would know whether you applied to two places or more. Don't do it. Colleges communicate with each other and any surreptitious activities will eventually be unearthed. Also, look at the Cons section for Early Action.

* Demystifying an aspect of EA and ED admissions:

One statistic often cited in favor of early application is that a greater proportion of students are accepted. This is a true statistic but the subsequent connotation that it is EASIER to get in via Early Action or Early Decision may not necessarily be true. The confounding variable (underlying cause) for the inflated proportion is the higher quality of students applying for early action and the greater commitment these students have for their first-choice school.

Rolling Admissions
Rolling Admissions works on a first come, first serve basis. The university gives you a deadline which you have to apply by (e.g. in February for the University of Michigan). However, you can apply any time before that deadline, and usually they will give you their decision after a few weeks (six weeks for the University of Michigan).

Unless you have a good chance of hearing positive news regarding an important contest or standardized test score, it is better to apply earlier via Rolling Admissions. That way you will know whether you are accepted or not and you will be able to plan accordingly. Also, towards the end of Rolling Admissions, most of the spots are taken and hence it may be more difficult to make that final cut.

Pros: You will hear back sooner than "regular" decision if you apply earlier. The pressure of the deadline is somewhat alleviated, which is good only if you have the motivation to not procrastinate.

Cons: As noted already, if apply too late, most of the spots will have been taken already, and you won't get in.

Regular Admissions
The office of admissions must have your application by a certain date (usually in January). You'll know their decision in April. The majority of the colleges that you apply to will fall under the category of Regular Admissions.

Pros: You have a bit more time to gather good news for the application and you don't have such a rigid timeline to follow.

Cons: The waiting. It may not seem like such a big deal now, but the waiting is really the most painful part.

For all admissions types, the deadline for informing the schools whether you are accepting or rejecting their offer of admission is May 1st. This applies to all nearly colleges.