The main difference between an unmanaged and managed VPS is that with an unmanaged VPS you have control over the server. This requires a lot of technical knowledge and if you do not know what you are doing or do not have the time then you can hire the services of someone that does. You will need to install and manage the software necessary for your website or programming to run as the owner of the server may only deal with hardware issues.
Most small companies find the unmanaged option perfect, particularly is they use an in house firm development or use any real time systems. However the costs can be quite extreme for large companies or those with very high profits and large companies tend to use managed VPS hosting. With enough profits the cost of using managed VPS is not large.
There are three main factors that will guide your decision when choosing a VPS; the amount of time it takes to deal with problems and complications, your profits and your technical knowhow. If you have any questions then you should address them to VPS companies or others that use VPS hosting. Read reviews written about the other companies as well to see how satisfied users are.
The owner of the unmanaged VPS hosting has several responsibilities such as dealing with networks, reboots and hardware maintenance. You may be only allowed a certain amount of reboots and you may need to wait until the owner is able to do a reboot.
If for some reason the server becomes infected and your software crashes well that is your concern and you will need to take steps.
The cost of an unmanaged VPS is much less than a managed because you are dealing with all operations. However you need to figure in the amount of time you spend on the VPS as the time cost may equate to paying more for a managed VPS.