I would put the three servers in three different locations. Now, if you had 60 servers, the sheer scale would require that you have a lot of them at a single location.
I'm actually in the same boat: I'm trying to decide on moving 90% of my operations into a local co-location. I have pretty much decided NOT to do this. Right now I'm spread out across five datacenters and I like that feeling. But it is very expensive to not have the economies of scale.
If you use good provider I don't really see how the datacenter is going to suddenly shutdown out of nowhere. If they go down sure all your servers go down but there is also the advantage of being able to get things cheaper if you're working with a large amount of servers. Also outages happen at every datacenter so going down for 15 mins in once a year or something is not the end of the world by any means. Of course if you're working with a good datacenter that has been around for a while IE: ThePlanet then I just don't see a reason to worry a whole lot about it shutting down.
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Just check out the facilities you are setting the servers up in. Unless you have the servers clustered with HA you will still have downtime should one of your DCs drop. You will get a better price rate if you rent a half/quarter cabinet in one DC and colo your servers. Anyone running a DC should have dedicated power drops and generators in place for automatic switching. That will cover the power issues and they should have a minimum of 2 dedicated providers for lines, most will have many more than that and run them with BGP so it won't matter if one goes down.