Both the MaxLine III and Caviar RE are intended for continuous operation, and therefore also a high MTBF. The Seagate 7.200, despite the high MTBF, is not made for this.
In my fileserver, I'm using one Maxtor DM9+ 200GB, one MaxLine III 250GB and one Seagate 7.200 200GB drive. They've been spinning 24/7 for about a year now, and none of them have had any problems what so ever Even though the high MTBF of some of the drives, cooling of the drives are very important, so you better make sure you've a couple of fans in front of them.
I think the Maxtor drives are pretty safe, especially the MaxLine III. It also have a 5 years guarantee