WD Red-series is a combination of WDs enterprise (RE4) drives, and Caviar-series value. Mainly designed for NAS builds (über RAID config 'n stuff), but can also be used as normal harddrive.
Seagate Barracuda is just a cheaper competitor to the WD Black-series.
Hard drives are one of (if not THE) most fragile component in my PC. In that regard, I would go for the Western Digital Red for the extended warranty and for the fact that it is rated to work 24/7 in NAS enclosures.
However, if that is going to be the only storage drive in your computer, the Barracuda is a little faster with its 7200rpm. So... yeah, it depends on what you plan on using it for.
Red drives aren't going to be as fast as Black drives, because they're made more for stability and to be run in RAID configurations. Get a Black drive instead. They're going to be the fastest hard drives you can get right now unless you want to blow the money on a Velociraptor which isn't all that much faster anyway.