Indeed there are different Hard Drive company.
In fact Buffalo doesn't manufacture hard drive. They provide the case only or the integrated solution for Online sharing, etc....(By the way, be sure if includes a hard drive inside and it is not just the case)
In fact there are few manufacturer of Hard Drive, but several resellers.
That would be very difficult to compare those, but basically:
Standalone hard drive:
Usually 2 types
1) 3.5 format. Bigger in size, bigger possible capacity, usually faster, cheaper but need power supply
2) 2.5 format. Very good for external hard drive for laptop, no need for a power supply (USB enough), but a bit more expensive and could be slower
You could have in USB3 or USB2. USB3 is the new standard and is faster if you have a USB3 port on your computer (But not so common except on new computers) and if the hard drive is fast enough
With USB2 the maximum transfert rate will be around 30Mb/s. A 700Mo movie transfert in less than 4 minutes.
With USB3, could vary a lot, but you could have 45Mb/s on 2.5 format, and may be 60-80Mb/s in 3.5 (Difficult to say, it depends on the hard drive inside the case)
For LAN hard drive, it is in fact usually called "NAS" for Network Attached Storage. It is like a tiny server with 1 or several hard drive(s). You can access it online, or at home on your local network.
They usually come up with some online/network adminstration tools (To easily configure it) and in some of them, they can even run some bitorrent clients, FTP, Mail server, etc...
A NAS is much more High tech than a simple hard drive and allow several computers to connect together and run some services, but is more expensive.
Speed are usually better than USB2 if you are connected on your 100MB network.
The most popular one are QNAP and Synology.
For example: http://shopping.pchome.com.tw/DRAF2U-162667681
(But is without hard drive)
In term of quality....well, the main point is what is inside the NAS or a Hard drive case. You could be a sony case with a crappy Western Digital hard drive inside... It is almost impossible to know..
So I suggest you to rely more on the warranty.
Why not buying in a computer shop instead ? More choice and better price may be?