Choosing the best diamond drill bits (see Wikipedia diamond tools) well suited for your needs depends on a number of factors. These factors will decide what variety and what manufacture you should choose and also how much does it cost you. The costs can vary depending on the type of drill you finally decide.
The variety of factors that you need to decide is primarily the type of material you are drilling and its various properties. These characteristics are the hardness of the material, the cost of the material being drilled as well as material thickness. The more the thickness of the material the more pressure and coolant you would need. That means the more specific type of diamond drill bit you would need.
The important factor is the drilling tool to be used and there are a variety of drilling tools available like the handheld drill or the drill press or the CNC drills.
Another thing is the frequency of use. That frequency may determine how much amount you are willing to spend. For example, if you are using it very often the electroplate bonded diamond drill bit if fine with you but if you are using it more regularly then the best option is the sintered one. Though the sintered ones are costly, but over the lifetime of the use, they may prove to be less expensive.
The third factor to consider is what the intended use of the hole is. That means whether you need a core or a plug or a proper hole and that in turn determine the kind drill bit you will use.
Based on the above factors you can actually do a cost versus the usage comparison to choose the best diamond drill bits for your needs.