Many people will argue about which DVR is the best. Honestly, they each have their pluses and minuses so arguing about "The Best!" becomes a moot point.
What does matter is what each platform offers and whether or not you need that feature.  That said, in many ways, each DVR platform also carries similarities. As much as they can differ, certain features are being added to multiple systems. This allows great expansion of what a DVR can do and can even change the definition of "DVR".
Below are some of the best DVRs available at the current time.

TiVo

Since the original launch in 1999, TiVo has become a household name.

A current TiVo Premiere DVR will cost you anywhere from $99 to $499 depending on the model and contract you select.  When compared to a service provider’s leased DVR, the upfront cost is much greater but with that you’re getting a much better experience.

Not only does TiVo provide a feature rich DVR experience, you get a lot of add-ons as well.  They have continued to add access to both local and internet content throughout the years.  Amazon VoD, Netflix and Pandora are just a few of the offerings provided with a TiVo device.

Something to keep in mind is that TiVo does charge a monthly service fee.

Windows Media Center

Microsoft’s platform has always been a niche product since its introduction.  The need to connect a PC to your TV has kept the software from going mainstream.  Also, even though computers have continued to drop in price, the cost of adding a digital ready tuner that receives the same channels as your service provider’s STB is quite high.

That said, using Media Center means that you can receive any kind of TV broadcast.  From cable, to over-the-air, all you need is the right tuner installed.  Since hard drives can be added at anytime, you never have to run out of recording space.

Dish Network

Much like Windows Media Center, SageTV runs on your PC and provides DVR functionality as well as other features.

More of a hobbyists software, SageTV has a bit of a steeper learning curve than Media Center.  The software does have excellent core functionality and an active community has grown around the product and has provided many extra plugins to extend the experience.

One issue Sage does have is that there is no native CableCARD support and that means no HD digital cable.  There are ways around this but again, it’s something for someone with some dedication.

Dish Network

Although you typically won’t find a provider DVR listed in a “Top 5” but when it comes to DVRs, Dish Network, and the below listed DirecTV have actually done a decent job.  Of course you’ll have to subscribe to the respective service in order to use their platform.

While you won’t find the functionality or extra features that you will on a platform such as TiVo, Dish Network’s ViP 922 does allow you to watch live TV or recorded TV on mobile devices anywhere you have an internet connection.

As well, unlike cable company DVRs, Dish has done a pretty good job of providing an easy to use and functional UI.

DirecTV

Much like Dish Network, DirecTV has worked hard to provide a decent UI for customers.  The company has also promised to launch a new TiVo-loaded device although when this will happen is still up in the air.

While DirecTV does offer mobile apps, they have yet to allow streaming of content to them.  As competition heats up in this space, you can bet it won’t be long before they do.

One advantage DirecTV has over competitors is the ability to use a single DVR to feed any TV in your house.  Their whole home service will provide TV to up to 15 other televisions.  This is something that many people have been asking for and while Time Warner has begun to roll out a whole-home service, it’s currently only available in their east coast region.