It is always preferable to opt for a managed hosting plan. In this case the web hosting provider provides with round the clock technical assistance, uptime guarantee and real time server monitoring. These are extremely important features as far as web hosting is concerned. Moreover as these factors are taken care of, the user can concentrate on the other essential factors of the business.
Well its always easier to have someone doing things you could probably do if you spend enough time searching for answers. But if you have enough money and time is crucial for you then managed servers is the way to go.
If you are familiar with OS and other softwares and got time to spend, you can choose unmanaged service. If you choose managed service, you have to check for good hosting providers who provides reliable support and services.
If you have a hosting expert than you can go with unmanaged server because your hosting expert can easily manage your web server and if you don't have a technical guy than you should go with managed hosting service.
It really depends upon how good you are in managing your servers. My company is itself a webhosting provider, so we of course have our own engineers managing the servers. But generally speaking, you should buy a managed hosting if you are going for a dedicated server or a VPS and specially if you are not well acquainted with everything related to their control panels. Anything could go wrong and at any time. Also, there are many things you would need to learn for instance, apache recompilation, DNS management, firewall configurations, latest updates and patches, and a sound knowledge of windows / linux. If you are not aware of these things, you should buy a managed server or you'll loose quite a lot of time and money fixing them.
if you have the time and the expertise, the unmanaged/self-managed server is attractive for those that want full control of the server. But that comes with the responsibility of maintaining the server, it also is the cheaper option. But the managed server allows you the peace of mind as everything is handled by the provider, although you have to make sure of their uptime and support.
I believe that managed hosting is what you should choose, if you want to save your valuable time to focus on the growth of your business. Though, un-managed hosting is cheaper than managed hosting, however, it will put the burden of managing servers and server management tasks on your shoulders.
If you are a real core technical guy Unmanaged server is the best as you have full access over the server and it does reflect the price... But if not I personally would say Managed server is the best..!!