Choosing the best multiband antenna for your purposes is a process that involves comparing what features you need with what cost you can afford. You will also need to determine how large of an antenna you will need to accomplish your desired aim or goal for the antenna. Ham radio or amateur radio enthusiasts often require a multiband antenna, and each of these individuals has different requirements as far as the cost, functionality, and size of the antenna, so there is not necessarily one best antenna for everyone.
Size is a key factor when selecting among multiband antennas. First, you will have to determine whether or not you have a place to store or mount the antenna you are selecting. You may also wish research any local building codes that would prohibit your antenna installation based on height, size, or other factors; some municipalities or homeowners associations place restrictions on sizes of external antennas such as these.
The size of the antenna that you choose will directly impact your ability to broadcast and receive signals from various distances, with larger antennas obviously providing a better range. You will need to balance the available space that you have with your requirements for transmitting and receiving power. Installation and mounting are also a factor in determining size, as larger antennas can be more difficult to install.
Cost is also a factor in determining the best multiband antenna for your purposes. A larger, more powerful, or more versatile multiband antenna will generally cost more than one that is smaller, less powerful, or less able to handle a variety of different frequencies or functions. Set your budget by determining what you can afford to spend on a multiband antenna and what your level of commitment to the radio hobby is before making your purchase; once your budget is set, you can search for antennas within your cost range that are of the appropriate size.
You will also need to determine what specific functionality you need in a multiband antenna. For example, if you live in a highly populated area, background interference, or “noise,” can be an issue. In an area with high amounts of background noise, you will need an antenna that is powerful enough to transmit despite this. You'll also want to make sure to choose one that has the proper filtering to remove some of this background noise so you can get a strong signal when receiving transmissions.