It really depends, with a colocated server, you have complete control over what parts go into your box, so the quality can be higher, but if anything fails on it, then you are generally responsible for it and it will cost you to have the datacenter replace it.
On the other hand, a dedicated solution belongs to the datacenter and THEY are responsible for any hardware that needs to be replaced. You also have a certain amount of bandwidth included for that price when colocation will actually cost more on the bandwidth side because you'll generally pay per Mb/s.