Windows 7 - External hard drive...recommendations anyone?

Been meaning to get an external hard drive for quite some time now and I'd better do it before I arrive at the "woulda, coulda, shoulda" stage. Of course the two biggest names in externals that I see are Western Digital (WD) and Seagate. Pretty sure I'll choose one of the two but I'm open to any and all suggestions. In fact, I wouldn't rule out getting TWO drives for that matter. Couple of quick questions. Which do you prefer? Desktop? Portable? Advantages and disadvantages of each? Also, what is "automatic backup" and how does it work? Does it follow your PC in real time and adjust itself in accordance to any changes made within the computer's hard drive(s)? I currently don't have USB 3.0, so that feature is not a factor but does it rule out the use on a 2.0 laptop? Please excuse all the rookie questions but I just want to get my facts in check before I pull the trigger on one (or more) external hard drives. Thanks and Happy New Year everyone!

I use this: Newegg.com - Aluratek AHDDS100F 2.5" / 3.5" eSATA & USB 2.0 External Docking Enclosure with 3Port USB 2.0 Hub

This allows me to swap out drives, I have one I use to keep backups on, another to store pictures and another to store other junk on.

The one drawback I see is it only works with SATA drives, no IDE support.

I also have one that works with IDE drives but I seldom use it anymore as more and more drives are SATA.

All I can say is avoid Seagate external drives. The enclosures aren't properly vented, if you leave it plugged in all the time, the heat will make the drive fail over time. After only a year, mine still works for about 30 minutes at a time, after which it gets i/o errors and cant be read. Then I have to unplug it to let it cool off before the computer will recognize it again.
This has really jaded me on external drives, don't know if I'll get another one. If you intend to use it for a network media drive(streaming movies to the xbox or whatever), or your going to be accessing it heavily, think about getting a second internal drive, or invest in a cooling pad to set it on.

I had an old 250GB SATA HDD and bought this. I don't use it all the time, so it spends most of its time plugged in and turned off, so no heating issues here. It's also been useful for getting files off of an HDD from broken pc for friends a few times. It's very easy to open, and is plug-n-play compatible; so it's much easier than hooking one up to my mobo. If you have an extra HDD, I'd suggest this solution.

Which Seagate are you referring to? The GoFlex portable or desktop? They also have the Expansion external hard drives. They also have a portable and desktop version. I like the idea behind the GoFlex as the interface can be changed from a 2.0 to an eSata by switching the cables. Too bad the eSata cable is priced separately.

I have 2 Seagate GoFlex portable drives. I've had them both for well over a year and have had no problems with them. But, what I use most is a Thermaltake Blacx. It is easy and quick to change drives and works great. It works with USB 2.0 and esata on 2.5" and 3.5" drives.

I have 7 different makes. They all work well. Hard to say which make to recommend.

If you want portability, take a 2.5" USB powered model. But for a desktop, a 3.5" model with its own power is better. I would not buy bigger than 1TB - rather buy a second one.

Right now all spinning disks are expensive because of the recent flood in Thailand. You may want to wait a couple of months - hopefully prices will come down. I would not pay more than $70 to $80 for a 750GB to 1TB model.

It's the Seagate Expansion 1tb, usb only(no esata) desktop model. Got it at best buy for around $150 last year.