Which is more standard in large enterprises: RAID5 or RAID10?
I work on directly on a customer base of about 2500 medium to very large businesses (think Sony-size), and currently RAID 5 is more common from what I see in their configs. That is, however, likely due to a few factors, like people still using older RAID controllers that don't support RAID10, people still thinking disk space is expensive, and the fact that with caching and such, web content often doesn't need to be sitting on a RAID 10 when a RAID 5 will do.
The most common configs that I see are something like RAID 5 for web content, RAID 1 for OS drives, RAID 10 for database data files, and sometimes a RAID 0 for something like tempDB.
RAID 5 vs RAID 10 isn't really an either/or thing. You need to look at the application and figure out what is best for the use case.
They both are. It depends on the application using the array, the number of disks in the raid group and the IO requirements of the applications sitting on them.
For example a file server probably doesn't need RAID 10 as the bulk of the data is just sitting there with a few users opening and closing files through out the day.
An OLTP database may need a combination of RAID 5 and RAID 10 while a data warehouse will probably need all RAID 10.
It shouldn't matter -- you shouldn't pick technologies because they're popular, you should pick them because they work. On the other hand, if you're trying to do a rigorous study on RAID levels, a question on serverfault isn't exactly the right way to go about it.
Having said all that, I would say that without a doubt RAID 5 is the more popular of those two choices. Plenty of hardware RAID cards don't support RAID 10 (although thankfully these are becoming far less common than they used to be), and lots of people don't like the idea of wasting half their disk space (because they're stuck in the days when disk platters were actually expensive).
I believe RAID 5 is increasingly considered nigh-on-useless, due to the time taken to rebuild a large array after a single disk fails, and the risk of a second failure (i.e. a catastrophe!) during this time.
We just switched to RAID 6 -- I considered RAID 10, but depending which second disk fails, that still feels prone to significant loss if a second disk fails during a rebuild...
"More Standard" isn't a clear enough question, certainly you'll find MORE R5 in large organisations simply because it's been around longer and is supported in more, and older, array controllers. R10/01 is however becoming more prevalent and important to those looking for consistent database performance.