Coming from more of a development background, revolving around database back ends, I would choose RAID 5+1 to host and protect my data.  With RAID 5+1 I get the benefits of the read speed of the multiple disk heads reading multiple pieces of information along with the mirroring of those disks.  Most database users are concerned with the speed at which the data is returned to them, so the users will have fast access to that data.  However, in a database environment, users can't afford to have the disks down for hours to repair if one of the disks in the array goes bad.  That is where the 1 (mirroring) comes into play.  If there is a problem with one of the disks in one of the arrays, the mirror would be in place and users would not know that one of the arrays is down.  This does have a downfall though, it would be quite expensive to have all the disks required to have this type of setup.  In an environment like a hospital this cost could be justified.  Hospitals are 24 hour a day operations and can't afford to have downtime outside of small windows of time. 

A daunting question limited to only your budget! As Dave stated there are many RAID configurations. However, in my current situation we use RAID 1 and RAID 5. The RAID 1 is used for the host operating system. Where the RAID 5 is configured for the 'DATA'. Incorporated in the RAID 5 is a Global Hot Spare to avoid any downtime that might happen during a failure. The Global Hot Spare automatically takes over for any other Hard Drive in the Array that shows possible failure. Then the failing Hard Drive can be inspected and/or replaced with a new Hard Drive. Thus becoming the new Global Hot Spare.

This configuration aviods downtime and allows the technicians time to correct issues. It works for us!

I would use RAID 5. It offers efficient storage, execellent security, and good performance. Plus, it is ideal for file and application servers. Two things that would be high on my 'concern' list.

I'm going to go against the grain on this one, to make this thread "interesting", RAID stands for Redundant Array of Inexpensive Disks. IF I was restricted to just one option I would go with RAID 1! My logic here is that RAID 1 requires at least 2 drives Vs RAID 5 requires a minimum of 3 disks. Choosing RAID1 would reduce hardware cost by 1/3. Most physical servers have a very limited role on the network, storage is required for the OS and a handful of applications. Given the rapidly increasing capacity of current hard drives there is NO real need to configures with RAID 5 for the additional storage capacity. For those who prefer to keep the system and data partition separate this can easily be configured within the OS.

With regard to redundancy my argument is that RAID 1 and RAID 5 essentially allow for the SAME level of protection against failure. in a RAID 1 configuration a maximum of 2 drives can fail before catastrophy (data unrecoverable). Although RAID 5 offers parity, it is also resticted to a maximum of 2 drive failures before catastrophy. From a pure cost and redundancy perspective I believe that RAID 1 is the way to go       

There is no clear cut answer between RAID1 and RAID5. It is really how the data is going to be used or accessed. RAID5, with more disks, would enhance the read performance. The RAID5 read performance increases as more disks are added to the array because the more disks are the more read/write heads there are, and RAID5 arrays have the ability to read simultaneously from all the drives, speeding read access. Since RAID1 only has two disk drives, and RAID5 has three or more disk drives, RAID5 has the read performance advantage.

I just read this article on zdnet and thought y'all might find it interesting.

(It is relevant)

http://blogs.zdnet.com/storage/?p=162

I will choose RAID 5 over RAID 1. The reason is because RAID 5 has more benefits than RAID 1. The first thing to factor out of this discussion is about pricing. As we all know, not any amount of money can pay for data. When we are talking about protecting data, I think the cost of hard drives shouldn't be a determinant. The tradeoff between the prices of using two hard disks versus three hard disks cannot be compared to the benefits derived from using RAID 5. RAID 5 has a lot of advantages which include higher data security, fault tolerance, high availability, etc.