WD and Hitachi merged, with Hitachi selling their 3.5" manufacturing to Toshiba - a condition regulators imposed to approve the merger. So your choices are Seagate, WD, and Toshiba. (Toshiba used to only make 2.5" drives before.)
Much is made of manufacturer reliability, but honesty there's more variability in reliability from model to model, than from manufacturer to manufacturer. And unless you're buying used (which I don't recommend), there's no real way to know the model's reliability until it's been on the market for a good 3-5 years. IBM (which Hitachi bought) used to make very reliable drives, then made the 75GXP which was one of the least reliable drives ever made, but then followed it up with the 180GXP which was again very reliable.
So buy whatever drive makes you comfortable, and use a good backup regimen to take care of reliability. Even the best drive can still fail, so a backup is crucial. And if you have backups, it's not really that big a deal how reliable a drive is.
Toshiba used to be very generous in their warranty - giving you credit which you could use to buy a new drive from their online store, instead of shipping you a refurb drive. But I don't know if they still do that.
Each manufacturer makes a variety of models for different purposes. The slower drives (5400 RPM, aka "green" drives) tend to use a bit less power and are fine for archival storage of things like movies and MP3s. The WD green drives tend to be temperamental because of issues with the spindown and/or head parking timeout. So for that reason I'd recommend Seagate or Hitachi if you're going for green drives.
The regular speed drives (7200 RPM) are suitable for a boot drive, but I would highly recommend you get a SSD for your boot drive. 120GB minimum, 250GB to be comfortable. The faster drives (10000+ RPM) I do not recommend at all - get a SSD instead. People make a big deal about the 5400 RPM drives being slow, but the 7200 RPM drives are only 1.33x faster. A SSD is 5x-100x faster (depending on size of the file). So if you're going to make a fuss about green drives being slow, then you shouldn't even be considering a HDD - get a SSD instead.
The SSHDs (with about 8GB of flash cache built into the drive) are a significant improvement over a regular HDD if you're using it as a boot drive. But a SSD is still much better. So again, I would recommend a SSD as your boot drive, and a "green" drive for mass storage. If you get a decent sized SSD and your motherboard supports Intel Smart Response Technology, you can even configure part of the SSD to operate as a cache for the HDD, effectively making it a SSHD if you plan to put frequently-read files (e.g. games) on the HDD.