They are two different beasts. A good match to your needs is more important than cost.
A rent-setup allows for certain "optimizations":
- Some will employ very simple security in the datacenter, because only their personnel needs to get in (no cages or locks)
- may run bare motherboards on ikea racks (no joke).
- elevated temperature thermal strategy - not too bad in practice, but you can't show it to customers
- run on specifically optimized power cirquits (12V DC directly to the mainboards)
- and of course they recycle servers (best way to tell: numer of run hours on the hard disk or old intel cpu model number)
- Not being geographically bound to your area opens up a lot more competition. If you don't care about the area, country, continent there are thousands of big and small guys.
- A bigger scale will get them cheaper servers and they'll always have spare kit somewhere.
None of these are inherently bad. Those practices makes them very competitive in giving you a machine and bandwidth. That's fine if that's what you need.
If you're happy with the services (and level of service) they provide there are few drawbacks.
By buying/renting rackspace (colocation) you can get the last word over a lot of things:
- you can drive up to the DC (often you'll have direct access) and inspect, reset or ritually curse machines.
- You can also perform migrations buy pulling disks out of machines, or moving machines to a different datacenter.
- Very specific setups (tricky routing, loadbalancers, ...) are often only possible with colocation.
- You can influence temperature by adjusting airflow (or complain and get more flow); but you will have to manage your own power draw.
- You can get complete control over 'backend' lans by buying your own switches
- Often you'll have more flexible wan options (dedicated vlan with 3 RSTP portchannels and failover routing to your rack? sure!)
- Depending on the situation you can get a better deal on bandwidth (in the bigger numbers) or add uplink providers.
- You're also generally responsible for generating the reset options, hardware maintenance/replacement etc. Including nights, during familiy dinners and on holidays.
- Meeting the owners/grunts face to face can get you a better understanding and other favors.
- If you dont have AC in the summer, you can sit in the hallway on a tile blowing cold air up your spine, surfing the net on a high speed ethernet connection pretending to uhhh repair backups